Grinding sound when decelerating - Page 2 - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Capt Spaulding · 03-24-2023, 08:18 PM

It’s probably completely off base, but I’ve had random rattles appear under the rear of the car at various times, but always on overrun. Traced to the aftermarket exhaust vibrating. Changing out the muffler bearings (exhaust mount donuts) to STI parts reduced it. Didn’t eliminate it, but significantly improved/changed it.

jaits · 03-25-2023, 03:46 AM

Anything is possible at this point. Can't really pinpoint where the sound is coming from exactly.

The shop also did a heatshield and exhaust inspection and nothing seems to be loose. But they found that one of my header bolts was stripped and had to drill a new hole to mount it back on. So the noise could be a leak from there.

But if it isn't getting louder or quieter over time then i think its best to just leave it as is. Maybe ill throw on a louder exhaust setup to over the sound :/ Not worth the time and energy over one of many sounds coming from this engine

wheelhaus · 03-27-2023, 01:29 PM

Sometimes this noise is caused by the unloaded gear teeth "rattling" inside the transmission or diff. I had the OEM clutch with Whiteline inserts at the trans, diff, and subframe, I noticed this noise very faintly only on occasion when decelerating between 3000-2500 rpm. However, after installing an Exedy Stage 1 clutch and OEM flywheel it got obnoxiously loud. Apparently, in my situation, the stiffer axial springs in the new disc hub was all it took to change the frequencies enough to allow this gear rattle to become more prominent throughout the entire drivetrain. A lightweight flywheel is also notorious for causing it because the reduced mass can't dampen these vibrations as easily.

Once I removed the bushing inserts from the trans and diff the noise has almost disappeared. Its still there, but MUCH quieter, virtually a non issue. Still not sure whether it was coming more from the trans or diff, but with all the searching I've done it apparently doesn't affect anything negatively. As much as I hate the idea of that, it's a somewhat common issue that never seems to actually cause problems, it just sounds like it is.

churchx · 03-28-2023, 04:52 AM

But such gear rattle always annoys as it "feels/seems like something is broken" .. i tried to live with that, but at the end gave up and reverted some bushings to have that noise gone. When i drive the car i'm minding warning indicators on dash and also abnormal noises. Even if some noise is not an issue, it introduced unneeded stressing about.

03-24-2023, 08:18 PM	#15
Capt Spaulding Persona Non Grata Join Date: Nov 2015 Drives: '15 BRZ (WRB) Location: On the Border Posts: 1,882 Thanks: 2,016 Thanked 2,781 Times in 1,200 Posts Mentioned: 10 Post(s) Tagged: 1 Thread(s)	It’s probably completely off base, but I’ve had random rattles appear under the rear of the car at various times, but always on overrun. Traced to the aftermarket exhaust vibrating. Changing out the muffler bearings (exhaust mount donuts) to STI parts reduced it. Didn’t eliminate it, but significantly improved/changed it. __________________ Slow is smooth, and smooth is fast

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03-25-2023, 03:46 AM	#16
jaits Member Join Date: Nov 2022 Drives: 13' brz Location: Canada Posts: 11 Thanks: 0 Thanked 4 Times in 3 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Anything is possible at this point. Can't really pinpoint where the sound is coming from exactly. The shop also did a heatshield and exhaust inspection and nothing seems to be loose. But they found that one of my header bolts was stripped and had to drill a new hole to mount it back on. So the noise could be a leak from there. But if it isn't getting louder or quieter over time then i think its best to just leave it as is. Maybe ill throw on a louder exhaust setup to over the sound :/ Not worth the time and energy over one of many sounds coming from this engine

03-27-2023, 01:29 PM	#17
wheelhaus Join Date: Jul 2012 Drives: 2013 BRZ, 2020 KTM Super Duke 1290R Location: Denver Posts: 1,788 Thanks: 714 Thanked 1,141 Times in 624 Posts Mentioned: 49 Post(s) Tagged: 1 Thread(s)	Sometimes this noise is caused by the unloaded gear teeth "rattling" inside the transmission or diff. I had the OEM clutch with Whiteline inserts at the trans, diff, and subframe, I noticed this noise very faintly only on occasion when decelerating between 3000-2500 rpm. However, after installing an Exedy Stage 1 clutch and OEM flywheel it got obnoxiously loud. Apparently, in my situation, the stiffer axial springs in the new disc hub was all it took to change the frequencies enough to allow this gear rattle to become more prominent throughout the entire drivetrain. A lightweight flywheel is also notorious for causing it because the reduced mass can't dampen these vibrations as easily. Once I removed the bushing inserts from the trans and diff the noise has almost disappeared. Its still there, but MUCH quieter, virtually a non issue. Still not sure whether it was coming more from the trans or diff, but with all the searching I've done it apparently doesn't affect anything negatively. As much as I hate the idea of that, it's a somewhat common issue that never seems to actually cause problems, it just sounds like it is.

03-28-2023, 04:52 AM	#18
churchx Senior Member Join Date: Mar 2015 Drives: 2014 GT86 Location: Latvia, Riga Posts: 4,333 Thanks: 696 Thanked 2,086 Times in 1,436 Posts Mentioned: 53 Post(s) Tagged: 1 Thread(s)	But such gear rattle always annoys as it "feels/seems like something is broken" .. i tried to live with that, but at the end gave up and reverted some bushings to have that noise gone. When i drive the car i'm minding warning indicators on dash and also abnormal noises. Even if some noise is not an issue, it introduced unneeded stressing about.

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