Resonance at around 70 MPH?

[Subie]

Originally Posted by brett_g

I can't believe this thread is this long. Have any of you guys actually owned cars with modified exhausts? It's exhaust DRONE it happens at certain RPM's /speeds. Sheesh. If you wanted a dead silent car, you shouldn't have bought this thing..

/sigh

If only you understood what was going on you would realize that this is not an exhaust noise. It's NOT ENGINE SPEED DEPENDENT. It's VEHICLE SPEED DEPENDENT. Get it? Got it? Good.

[russv]

I went out and did the 35 mph and 70 mph sound test and noted the sound described at both speeds. It seems to come from the rear of the car. I think there are 3 possible theories:

1) The tires create the harmonic which is then amplified through the body of the car.
2) The exhaust creates the harmonic
3) The rear differential creates the harmonic

I'm tending to rule out the tires as the harmonics are at differing speeds. (My opinion, I could be wrong).

Having owned rear wheel drive cars in the past I have experienced drive train noise. Consider that you are dealing with 3 components: transmission, drive shaft, and differential.
I've also experienced cars with exhaust systems that demonstrate a harmonic sound, but it is usually over a certain RPM range and not necessarily speed related (Mini Cooper, various Hondas).

My money is on the drive train, probably drive shaft/differential. That said I am not too concerned at this point, unless it gets worse. Probably a normal sound.

AND, let's keep the discussion civil because it appears to be endemic to all our cars and is a concern to some.

[industrial]

I've tried to listen for this resonance. I don't notice it at all.

[Subie]

Originally Posted by russv

I went out and did the 35 mph and 70 mph sound test and noted the sound described at both speeds. It seems to come from the rear of the car. I think there are 3 possible theories:

1) The tires create the harmonic which is then amplified through the body of the car.
2) The exhaust creates the harmonic
3) The rear differential creates the harmonic

I'm tending to rule out the tires as the harmonics are at differing speeds. (My opinion, I could be wrong).

Having owned rear wheel drive cars in the past I have experienced drive train noise. Consider that you are dealing with 3 components: transmission, drive shaft, and differential.
I've also experienced cars with exhaust systems that demonstrate a harmonic sound, but it is usually over a certain RPM range and not necessarily speed related (Mini Cooper, various Hondas).

My money is on the drive train, probably drive shaft/differential. That said I am not too concerned at this point, unless it gets worse. Probably a normal sound.

AND, let's keep the discussion civil because it appears to be endemic to all our cars and is a concern to some.

1) From past experience with tire noises, there is at least some change in the character of the noise depending on the road surface. I've noticed none on all the different pavement types I've driven on, including rough asphalt, smooth asphalt, concrete, etc.

2) The noise does not sound at all like it's coming from the exhaust to my ears. I have not tried clutching-in at 70 MPH to see if there is any change in the character of the noise, but I am extremely skeptical that there would be. Also, you are reporting the noise with an automatic transmission vehicle and I am seeing it with my manual transmission; the difference in gear ratios would mean that the engine is spinning at different speeds between our two cars. For us both to hear the noise at the same speed seems to rule out the engine (and my extension, the transmission and the exhaust) from being the culprit.

3) I don't recall if the final drive is a different ratio between the automatic and manual cars, but regardless, that is only one component of the differential. The LSD itself is the same. I, like you, tend to think the noise is coming from the differential or another component in the driveline.

It should not be too difficult to identify the source of the noise if we can get Subaru/Toyota interested in doing so; as I have stated before, I do not feel that the noise is normal and will insist upon it being addressed.

Originally Posted by industrial

I've tried to listen for this resonance. I don't notice it at all.

This is but one reason why I don't buy that the noise is normal.

[russv]

Originally Posted by industrial

I've tried to listen for this resonance. I don't notice it at all.

My ears are pretty sensitive to car sounds so it's something I notice. It could just be a natural resonance from the body. I'm at a bit of a loss.

[Bacon]

Originally Posted by Subie

Good noises, not bad ones.

I suppose you enjoy the DI cricket sound, and the rear deck tapping/popping sound? Because race car?

I dont own a BRZ or FR-S. Performance cars of this price bracket generally make all kinds of noises.

[Stu baru]

My BRZ does this, and to my ear it's front-end located, possibly more on the left than right. I only notice it when I get up to speed, but found it hits heavily in 6th cruising in the 50's. My car's at the detailer for two days getting Opti-guarded and window tint installed, but I'll do so more evaluation and post back what I find. It's not wheel bearings, those are constant, more of a whine, and increase in pitch and intensity with speed. This is definitely something harmonic going on that relates to the speed of the vehicle.

[ahausheer]

A wheel thats out of balance will do something similar what you are describing with the harmonic at multiples of a set speed. Usually you feel the tire bouncing but perhaps the suspension is soaking it up. Only the wheels, tires, and bearings, are speed dependent, everything else is rpm dependent. The differential rpm dependent.

[Stu baru]

Originally Posted by ahausheer

A wheel thats out of balance will do something similar what you are describing with the harmonic at multiples of a set speed. Usually you feel the tire bouncing but perhaps the suspension is soaking it up. Only the wheels, tires, and bearings, are speed dependent, everything else is rpm dependent. The differential rpm dependent.

Interesting point, and one that would make sense given what I'm hearing. I don't feel a balance issue, but that could still be the cause. She's going in for her complimentary first oil change soon, and I'll mention this to the service folks and may have them do a tire rotation to see if the sound changes location to my ear.

[Subie]

Originally Posted by Stu baru

My BRZ does this, and to my ear it's front-end located, possibly more on the left than right. I only notice it when I get up to speed, but found it hits heavily in 6th cruising in the 50's. My car's at the detailer for two days getting Opti-guarded and window tint installed, but I'll do so more evaluation and post back what I find. It's not wheel bearings, those are constant, more of a whine, and increase in pitch and intensity with speed. This is definitely something harmonic going on that relates to the speed of the vehicle.

I wouldn't call this noise a whine; it really does sound like a tuning fork like ruskymx describes.

I've scheduled another appointment with my dealer for next week, but it may get pushed out if SoA & my dealer jointly decide to wait for the district rep. to come before reevaluation my car. I'll keep you all posted on any new developments, and those that I asked to contact SoA, please do so if you haven't already.

[pinoyplaya]

Mine smells like rubber. Not sure if that's normal for a brand new engine. But it seems like something was burning for sure.

Havent notice any chirping yet.

[SuperDave]

Originally Posted by Bacon

I dont own a BRZ or FR-S. Performance cars of this price bracket generally make all kinds of noises.

TROLOL!

[nibor33]

I was just reading this thread for the first time (because I don't have the noise). I couldn't help but think it was tire, or wheel & tire balance related. If there is an imperfection in the tire or it is out of round, or the balance is off, it could cause what you are experiencing. Sometimes if that type of problem is on a rear wheel you don't feel the vibration.

I know the dealer SHOULD be the one to diagnose it, but I often find myself (more patient, more concerned) doing their work for them. Here is my suggestion to the OP: switch your wheels front to back. This will eliminate wheels and tires as a possibility if the problem remains in the rear. It is a very easy thing to do yourself, consider it quality bonding time. And, who knows, if the noise moves, you found the problem.

HTH.

[Bacon]

Originally Posted by pinoyplaya

Mine smells like rubber. Not sure if that's normal for a brand new engine. But it seems like something was burning for sure.

Havent notice any chirping yet.

That burning smell is something all new cars do. Itll go away soon enough.

Originally Posted by SuperDave

TROLOL!

[ruskymx]

Could it be something under the car like a splash shield that has a designed hole in it and when the vehicle reaches a certain speed it makes a noise like blowing over the top of an empty beer bottle. Actually, that's kinda what it sounds like but you can feel it in your feet through the pedals.

Btw, didn't get a chance to call SoA yet. Will do so tomorrow. I just can't have any warranty work done until I get flashed back to stock. Currently testing for Visconti's stg1 tune.

[Subie]

Originally Posted by ruskymx

Could it be something under the car like a splash shield that has a designed hole in it and when the vehicle reaches a certain speed it makes a noise like blowing over the top of an empty beer bottle. Actually, that's kinda what it sounds like but you can feel it in your feet through the pedals.

Btw, didn't get a chance to call SoA yet. Will do so tomorrow. I just can't have any warranty work done until I get flashed back to stock. Currently testing for Visconti's stg1 tune.

Listening to the noise and its cyclical nature I don't think it can be anything but a driveline component/bearing of some kind. I spoke again with SoA today but the actual representative with whom I dealt when I initially called will hopefully call me back tomorrow. I appreciate the follow-through on your part.

[baadshah]

Did you check for this?

[Subie]

Originally Posted by baadshah

Did you check for this?

When I picked up the car I did and they were already installed. The absence of those plugs would not cause this type of noise anyway.

[baadshah]

Tried this?

[Subie]

Originally Posted by baadshah

Tried this?

The sound isn't coming from the engine.

[Stu baru]

So I picked up my car from the detailer after work yesterday and noticed that the pattern of occurrence of this has changed. The 50 mph zone is less dramatic, and a bit more intermittent. This is interesting, in that the detailer removed all the wheels to clean and Opti-Guard them. I've not contacted him yet to see if they went back on in the exact same locations or not, but this might imply tires, alignment, and/or balance as a source. I need to do some evaluative driving to see what the new sound pattern is. She goes in for her complimentary first oil change Saturday and I've already alerted the service department that I want to demonstrate this and the DI chirp. More as it becomes known...

[alan329]

You should ask you dealer to look this up.

Service Bulletin # 05-50-10R
Noise, Vibration and Harshness (NVH) at Highway Speeds Caused by a Tire Imbalance or Excessive Radial Force (revised)