My BRZ rattles while rolling in neutral (video)
 

My manual transmission 2014 BRZ makes a rattling/flapping noise sometimes between 5mph and 30mph when I am rolling in neutral. The most difficult thing about this noise is that it seems to happen randomly, sometimes it happens and sometimes it won't happen. Here is what I've noticed:

The noise sometimes happens while I'm braking
The noise sometimes happens when I'm NOT braking
The noise sometimes does not happen at all.
The noise only happens in neutral at idle RPM
The noise happens while driving straight, not turning
The noise sounds like it's coming from under the hood in front of the driver
The noise started happening around 4000 miles on the odometer
The noise started happening once summer began and I used the A/C more often
I've never heard the noise happen when the A/C is turned OFF (I need to test this more)
The idle RPM seems fine when the noise happens (tachometer reads ~600rpm)
The shift knob does NOT rattle with the noise
The car doesn't shake with the noise

Here is a video of the rattling (you will need to turn up your volume to hear it).
[ame="https://www.youtube.com/watch?v=xWO3pzi1ICU"]Manual BRZ flapping rattling noise while rolling in idle - YouTube[/ame]

I suspect that the rattling is coming from the compressor for the A/C turning on while the car is rolling in neutral at idle rpm. Maybe the compressor lags on the engine and causes that flapping noise. The workers at my Subaru dealership couldn't figure out what was causing this noise. However, one worker who rode with me thinks the noise does not sound mechanical, rather it sounds like something is flapping around. We agreed that I would check back with them later, and if the noise continues or gets worse, we would test drive a BRZ on their lot to see if other BRZ's make that noise. I have made no changes to my BRZ besides a K&N air filter and mudflaps, but I'm very sure neither of those things are causing the noise.

My questions are:
Does anyone else's BRZ/FRS make this rattling noise?
Is this rattling noise a symptom of a serious problem?
Can this rattling be ignored, like we ignore the idle chirping/cricket noise?
Do you know what is causing this noise?

Thanks

hmmmm.......just curious ..... why are you "rolling" in neutral..??

Does it do it with the clutch in & out or just one way .. ??

As far as your questions, I's say:

1 - mine doesn't make this noise (of course I'm old and half deaf)
2 - I doubt it
3 - oh, yes ....especially if your half deaf
4 - sorry, I have no idea

I hope you get it figured out ......:)


humfrz

Thanks for your response. I'm rolling in neutral because of my driving technique with stick. For example, if there is a red light ahead, then to slow down I will put the car in neutral and apply the brakes (the other method would be do downshift through each gear as you slow down, but I prefer to just leave it in neutral). I don't leave my foot on the clutch while the car is rolling in neutral, I remove my foot from the pedal completely once the car is in neutral.

I also doubt that the rattling noise is a serious problem. But I'm a little worried because I don't know what the noise is and I haven't found anyone else who has the same problem.

I'm apparently too old, because I couldn't hear it :(

Sorry, the video is very quiet because my dashcam doesn't record audio very well. But I can hear it when I turn my speakers very loud.

The best way I can describe the noise is it's like when you accidentally lug the engine from letting the RPMs drop too low while the car is in gear. Except when I hear my BRZ rattle like that, the BRZ is in neutral and the RPMs don't seem to be dropping low at all (staying around 600rpm). Furthermore, neither the car or shift knob rattles when the noise happens.

I've experienced the same thing when coasting in neutral. I don't have a solution, nor am I a mechanic, but I have wondered if the car idles lower than it should. I've seen the rpms drop as low as 400 and then sputter back up to a decent idle of 6-700. I'd be curious to hear what folks with more car experience have to say.

I will hear this when revs are low & I'm creeping at a slow pace with a lite foot on the accelerator pedal - it's that noisy gearbox. I just changed my gearbox oil & it's much quieter now, shift is still ordinary when cold but definitely quieter !

No need to roll in neutral from those speeds. You'll save gas by leaving it in gear when coming to stoplights, just downshift to the appropriate gear and clutch in when your rpm's reach 1100 rpms.

There's no need to downshift through every gear coming to a stoplight.

And you're clutching in like a 100 feet before the light. Is that your normal driving style? You can clutch in much closer to your braking point, just get your timing right.

I usually downshift one gear, but sometimes maybe 2 gears if I'm in too high of a gear. And try and roll as slowly as I can towards red lights. This saves gas over approaching an intersection as fast as you can and then making your car idle in neutral, or rolling as you're doing it.

I've been driving stick for 6 years and I always thought it saved gas by going into neutral instead of leaving the car in gear. But now that I think about it, if the car is in gear while rolling, then the rolling of the wheels is what keeps the engine revving and perhaps this uses zero gas. On the other hand, if the car is in neutral while rolling, then the car is using a little bit of gas to keep the engine revving at idle RPM. I also found this article that supports your claim: http://www.popularmechanics.com/cars...l-fuel-economy


Thank you for enlightening me.

When I run A/C and the compressor kicks in at idle the RPMs will dip a little and it does make the feeling of engine lugging. I believe it's completely normal, it's just spinning up the compressor from a dead stop at idle RPMs where there's little available torque. If you want to see if that's what's causing your exact noise, warm up the car fully (so the RPMs will idle normally since they idle higher when cold), park, and hit the A/C switch and turn the temp all the way down to force the compressor on. See if that replicates your sound.

And yes, when you decelerate it's deceleration fuel cut that triggers. If you ever have an OBD2 app running while driving you'll notice AFRs shoot to the top of the scale since there's no fuel being injected and the momentum of the car keeps the engine spinning.

Mine does this as well. I read somewhere else on the forum that it's the flywheel rattling when the RPMs drop too low. I asked on the scion site if it will damage the flywheel but no response yet.

Also, since I first noticed it, it has been getting louder and more frequent..

I have heard many noises come out of my car due to mods etc but I have not heard that exact one.

Our stock flywheels are damn near silent - although, mine is aftermarket and that is exactly the RPM range where it does chatter. My chatter is a higher pitch/frequency though.

Mine does this exact thing too, I never made the connection that the A/C condensor could be responsible. Ive noticed it for a few weeks now and I always chalked it up to flywheel noise or some other driveline related noise. I noticed with mine though that the noise will occur more frequently when in neutral and slow/brake quickly to come to a stop. If I coast for a while and come to a stop slowly and smoothly, the noise almost never occurs. Also, when the noise happens my rpm needle dips a couple hundred rpms, so it must be at least indirectly related to something running off the pulleys.

I haven't yet been able to witness the RPMs dip when the compressor kicks in (my eyes are usually on the road not the tachometer whenever I hear the rattle), nor have I been able to purposefully cause the rattling sound by switching on the A/C while in idle. Maybe it will help if I turn the thermostat down to LO before I turn the A/C off, wait a while and let the car warm up, and then turn it back on while in idle. I've never heard the rattle while idling at a dead stop though, it only happens around 5 to 35mph. Sometimes its loud, sometimes it is very quiet or barely audible.

The rattling noise appears to be normal
 

I found the thread: http://www.ft86club.com/forums/showthread.php?t=12429

I'm ashamed I didn't find it before posting my own thread, but I did try searching the forums before posting.

Here is a video from that thread that shows the exact same noise that I am experiencing, and it also shows that the tachometer needle DOES drop to about 600rpm and jumps back to 700rpm when the rattle stops.
http://s421.photobucket.com/user/whs..._1331.mp4.html

After reading through all 5 pages of the thread, most people are blaming either the direct injection system, lightweight flywheel, throw-out bearing, gear box, or just harmonic oscillations for the chattering noise.

Furthermore, there is no solution to this noise yet and we probably don't need to be concerned about the noise. As long as we keep telling dealers that we are experiencing this noise, I think the word will get to Subaru/Toyota and they might give us an answer. For the meanwhile, the chattering noise seems to be completely normal, happens to most if not all BRZ/FRS's, and most likely will not damage our cars.

Thanks everybody for your responses.

During engine braking the computer cuts the fuel supply. When just idling (which is what happens when you're coasting in neutral) the computer has to feed fuel to the engine to keep it running. I have my doubts that it really saves you enough fuel to make any significant difference though.

That's not why some of us downshift. A performance car actually handles differently when it's in gear. When coasting out of gear, I don't feel like I have complete control of the car, nor am I or the car ready for unexpected situations that might require immediate maneuvering. Take your car to an empty parking lot and try slinging it around a bit in gear and then while coasting, and you'll feel the difference.

There are also some good arguments regarding the way gears wear that support engine braking. If you're always applying power to gear teeth from the same direction, they can wear unevenly. Engine braking evens out the wear pattern so that the teeth last longer and bite better, or so the argument goes.

I have this as well. Its Engine cutting off fuel. Happens even after my OFT stage 1 reflash.

I agree that the mpg difference between coasting in gear and in neutral is
insignificant. Tools might read about 300mpg for neutral and 9999mpg for in-gear, however, idling in neutral might only consume one gallon per hour. And the time I spent coasting in neutral was not very much, only a few seconds before every stop. So maybe coasting in neutral might cost only $15 to $20 extra in gasoline for an entire year.

That's an interesting point you made about gear wear, I never knew about that. Some people believe that leaving the car in gear while coasting may slightly increase wear on the engine (instead of wearing on brake pads in neutral), which would make coasting in neutral a better choice. But the extra wear on the engine is probably next to nothing.

Thanks for posting. I believe I made a thread asking the same question but it was disregarded. I'm surprised not everyone has noticed this yet as I hear it often, especially when I'm coming to a stop from a downhill and I put it in neutral a bit earlier. Seems like a 10% chance in these situations.

So stop putting it in neutral from 30-40 mph.

When coasting in neutral at any speed you have taken your car and turned it into a big, heavy (relatively),expensive (again relatively) soap box racer!
As soap box racers are not generally know for their handling, speed (other then down hill) or ability to avoid sudden changes in the driving situation or conditions you are usually better off to have the car engaged in the appropriate gear at all times. I know that accelerating quickly or a sudden swerve under power has saved my butt as many, or more times, then hammering on the brakes and if I was coasting in neutral those times I would have been screwed.

Mine does this as well, only when the AC is on.
The rpm get's so low, the daytime running light turn off sometimes. I saw this happening several times in the reflection of the car in front of me.
It's just annoying, as long as it does not stall...