Loud Noise When AC Is On?

[Bushhy]

[ame="https://www.youtube.com/watch?v=2WK0FNVT9h0"]BRZ Idle AC noise? - YouTube[/ame]


So this noise started recently. I have been trying to figure it out. Clutch is stock and was replaced about 9k miles ago when my Transmission was replaced. The only way to stop this noise is to:


1. Turn off AC
2. Push in Clutch


Anyone have any ideas? I cannot figure this out for the life of me.

[humfrz]

To me, it just sounds like the A/C compressor being engaged ....


humfrz

[Bushhy]

Originally Posted by humfrz

To me, it just sounds like the A/C compressor being engaged ....


humfrz

Now why would it get quiet when the clutch is pushed in? Thinking of raising my idle and see where it goes

[DirtySouth86]

Originally Posted by Bushhy

Now why would it get quiet when the clutch is pushed in? Thinking of raising my idle and see where it goes

Weird, I would say clutch release bearing, but not sure how the ac would have any effect on that, so I may be off base there.


Raising idle? Are you tuned? This car's idle is controlled by the electronic throttle body and the ECM. The only way to adjust idle speed would be with a tune. Why do you want to increase idle speed? what is your current idle rpm? Does the noise go away if you just barely rev the engine (100-200 rpm)?


There is a TSB for ECM reprogramming to help correct idle instability with ac on and extended crank time, but not sure if it would have any effect
on the noise.


Scion just released a TSB for the clutch release bearing as well. Not sure if Subaru, has the same TSB yet though.

[humfrz]

Originally Posted by Bushhy

Now why would it get quiet when the clutch is pushed in? Thinking of raising my idle and see where it goes

Let me guess ...... when you turn the A/C ON, the engine is under more of a load and makes that sound ...... when you push in on the clutch, the engine is relieved of turning the shaft in the transmission, thus speeds up just enough that the sound goes away .......

Calling @Ultramaroon for comment ....... although, NOT saying that humfrz is "out to lunch" .........


humfrz

PS - Bushhy, I suggest you go down to your local indoor firing range and ask to test fire a .357 or .44 mag revolver (use no ear protection). Then you won't notice half the weird sounds that the FA20 engine makes ......

[Ultramaroon]

Originally Posted by humfrz

Let me guess ...... when you turn the A/C ON, the engine is under more of a load and makes that sound ...... when you push in on the clutch, the engine is relieved of turning the shaft in the transmission, thus speeds up just enough that the sound goes away .......

Calling @Ultramaroon for comment ....... although, NOT saying that humfrz is "out to lunch" .........


humfrz

PS - Bushhy, I suggest you go down to your local indoor firing range and ask to test fire a .357 or .44 mag revolver (use no ear protection). Then you won't notice half the weird sounds that the FA20 engine makes ......

I bet this is just the "neutral rollover" sound.

Because this is a little four-banger, at idle, especially if the engine is doing work like running the AC, it doesn't rotate perfectly smoothly. It could be eliminated by installing a heavier flywheel but who wants that?

With a constant-mesh transmission (all manual transmissions) all the gears are driven all the time. We only pick which pair of gears is engaged to the output shaft.

There's always a little backlash between the rotating components. Just take my word for the fact that it has to exist. Everything just rattles a little in neutral.

Sometimes we can narrow down to which pair of gears is making the most noise by introducing a little bit of drag. While it's making the noise, gently nudge the gearshift into each gate a tiny little bit. Don't hold it there. Just a quick gentle nudge and listen for a change in sound. Don't squeeze all the oil out from between the baulk rings in the syncros.

Bushhy, Let us know if that confirms anything.

[stevesnj]

[Sapphireho]

Mine is doing the same thing. Just noticed it today, probably because I haven't used the a/c in awhile. Coming home from summer kickoff, we get off the freeway, first light, a/c cranking, stop, put in nuetral, sounds like a box of marbles. Push in the clutch or turn off a/c, goes away.

Sound is loud and awful.

Does anyone have a "for sure" answer? Ultra's makes sense, especially since I have a lighter flywheel.

Btw, a 2015 owned 2.5 years, never heard it before.

[Joon525]

Originally Posted by Sapphireho

Btw, a 2015 owned 2.5 years, never heard it before.

Amazing, on my 2016 I heard it the very first day I drove it off the lot.
(I don't care anymore unless someone figures out exactly what it is)

[ZX88]

Same issue here only when the A/c is on. For me its pretty intermittent. I notice it more on hotter days. I pretty much have the A/C on all the time.

[Sapphireho]

Today, not a sound. Yesterday was the first time I have ever heard it, but I was in "the valley of the devil". I don't think my car has ever been that hot.

I think I stated my last response wrong. My "for sure" list was more a wish for an expert to say it's ok.

[SaulSNES]

Hate to bring this back from the dead, but I havent been able to find much (if any) information on what could be the cause of this and a possible solution. Im experiencing the same sound with the AC on, dissapears when I push the clutch in and only hear it when its idling. I thought it maybe had something to do with the lightweight crank pulley, flywheel and driveshaft I recently installed but im seeing that even stock twins are experiencing this noise.

And. Its. Driving. Me. Nuts.

Any leads would be greatly appreciated!

[Ultramaroon]

Originally Posted by SaulSNES

I thought it maybe had something to do with the lightweight crank pulley, flywheel and driveshaft I recently installed but im seeing that even stock twins are experiencing this noise.

And. Its. Driving. Me. Nuts.

Any leads would be greatly appreciated!

It's perfectly ok. As I said before, it's just gearbox rattle. You made it more obvious with the lightweight flywheel.

[SaulSNES]

Originally Posted by Ultramaroon

It's perfectly ok. As I said before, it's just gearbox rattle. You made it more obvious with the lightweight flywheel.

I appreciate that man!