Grinding sound when decelerating

[IVRafa]

Hey guys,

I just got a used 2018 Toyota 86 a couple of days ago and noticed this sound coming from under the car when decelerating at around 3500 - 2500 RPM. Pushing the clutch in seems to get rid of the noise.

Here's a good clip of someone I found with the same problem:
https://drive.google.com/file/d/1iMZ...ew?usp=sharing

So I've seen a couple other topics regarding this on the forum but:
1. They all seem inconclusive
2. None of them have sound clips

If I had to describe it, it sounds like a mix of a grinding noise combined with the noise your engine makes when it starts to lug (without all the vibrations).
Some of the other threads describe a "Jar of marbles" sound, but this doesn't sound like that to me. I've also looked at videos of bad TOB sounds and this doesn't sound like that either.
This is my first manual car so no idea if this sound is normal or not but I don't notice anything wrong with how the car drives. Can shift smoothly into each gear, no problems with the clutch either.

Any help would be appreciated!

EDIT:
Compiling other threads that seems to have the same problem (again no sound clips so can't be totally sure)
https://www.ft86club.com/forums/showthread.php?t=15186
https://www.ft86club.com/forums/showthread.php?t=8344

The consensus from those as well as from some 86/brz facebook groups is that the sound is normal.

[blsfrs]

Check/change your tranny lube. Motul is considered to be the best by many who think their opinion is important.

[soundman98]

if you just feather the clutch slightly(1/8 pedal press, ie; ride the clutch), does the noise go away, or only when pushing the clutch all the way in?

[IVRafa]

Originally Posted by soundman98

if you just feather the clutch slightly(1/8 pedal press, ie; ride the clutch), does the noise go away, or only when pushing the clutch all the way in?

It only goes away when I push the clutch all the way in.

I'm going to change the trans and diff oil to Motul Gear 300 and see how that affects the noise levels.

[Ultramaroon]

Originally Posted by blsfrs

Check/change your tranny lube. Motul is considered to be the best by many who think their opinion is important.

Pshhh... What do they know?

[soundman98]

all the way in would indicate transmission or driveline, as the clutch is disengaging those.

i would inspect the rear diff and the drive shaft first. specifically the rear diff gear lash.

[IVRafa]

Originally Posted by soundman98

all the way in would indicate transmission or driveline, as the clutch is disengaging those.

i would inspect the rear diff and the drive shaft first. specifically the rear diff gear lash.

I actually think you're right on the money with this. Been researching on some rear diff sounds and came across this video:

And his car does something similar when he lets off the throttle. He had to get a full rear diff rebuild

Just waiting for the motul 300 gear oil I ordered before changing the diff fluid. Really hoping that quiets it down. The last change was done 6 months ago (and only 2k kms driven since then) so if I find a lot of gunk on the drain bolt I think that's another sign somethings going wrong.

If the fluid change doesn't work then I'll probably have to find a mechanic to check the rear diff backlash and pattern.

[blsfrs]

A grossly subjective lash test would be to jack the car up and twist the drive shaft back and forth. There should be only a slight bit of play when you change the direction of twist. The technique is not too scientific but that's where we started in the old days.

[IVRafa]

Originally Posted by blsfrs

A grossly subjective lash test would be to jack the car up and twist the drive shaft back and forth. There should be only a slight bit of play when you change the direction of twist. The technique is not too scientific but that's where we started in the old days.

Will give that a try as well once I get my jack stands!

[IVRafa]

Updating this if ever someone with the same problem has the same problem.

Just did a full fluid change:
H-tech 100 plus 0w20
Motul Gear 300 75w90 for the transmission and rear diff

And the noise has not really gone away (Shifting feel however is much better!). My old transmission oil was still in pretty good condition. However my rear diff was pretty dark and had a lot of sludge stuck to the magnetic drain bolt.

I just got used to the noise honestly. You can only hear it on low rpms with the windows closed and no music. Just gunna assume it's nothing unless it gets louder.

[TurboLag23]

Check to see if the car has any aftermarket transmission mounts. My Whiteline one makes the transmission noise very pronounced, especially while coasting.

[mav1178]

when I had my car there was a faint sound, only noticeable under WOT.

turns out, a small part of the stock heat shield was rattling. it only vibrated during certain RPM ranges.

went away after I put headers on. went away after I sold the car.

[jaits]

Digging up an older thread since I've also had this noise issue when decelerating at around 2000rpm. Posted a threat but received no reply so I wanted to know if you have an update on the noise.

My noise only occurs when the car is in operating temp. I have done some testing on my own to determine the noise came from the passenger engine bay area; most notably the near the coil packs. I have also taken it to a shop where they had suspected it was due to valve clearance issues. I being OCDed caved in and fix the clearance issue but the noise didn't go away. So now I have given up chasing this sound and just enjoying the car with the windows down and blasting music lol

[jaits]

Originally Posted by jaits

Digging up an older thread since I've also had this noise issue when decelerating at around 2000rpm. Posted a threat but received no reply so I wanted to know if you have an update on the noise.

also forgot to mention, I have gone through the same route before the valve clearance fix and changed the trans fluids with redlines but again, the noise didn't go away.

My car is fully stock too. Maybe it's the back pressure from the exhaust? Maybe an exhaust could fix it who knows...