[pcelenta33]

Hello Friends,

I recently got a 2020 ZLE M6 and it's currently at the Chevy local dealer.

I brought the car in for a strange noise coming from the rear end of the car. Here are the details...

-Roaring/Whining noise in the rear, honestly have never heard anything like it.
-Noise occurs ONLY under deceleration, no throttle, no brakes
-Occurs at all speeds and gets quieter as you decelerate
-It did not seem to impair any driving ability, all gears were working, no grinding in the midsection or upfront.


The car has been there 6 weeks now and this is what the dealer has done to my knowledge...
-Replaced the Diff
-Replaced one of the control arms and respective bushings, not sure why, this would not have been my first guess.

Now they are talking about getting it to a transmission tech, but I really don't understand how it could be that. I'm going to be heading to the dealer tomorrow to get some more answers, I haven't seen the car since I dropped it off so I am getting antsy as you could probably imagine haha

Any thoughts?

[LT4Greg]

I would go back and get the car and drive it until something happens or breaks. Your warranty should cover any repairs needed if and when something does happen to your ZLE!

[pcelenta33]

Originally Posted by LT4Greg

I would go back and get the car and drive it until something happens or breaks. Your warranty should cover any repairs needed if and when something does happen to your ZLE!

Honestly you have the right idea... it's been there 6 weeks now and I just think it's getting a little out of hand. I appreciate the input.

[taylorforschool@gmail.com]

Originally Posted by pcelenta33

Honestly you have the right idea... it's been there 6 weeks now and I just think it's getting a little out of hand. I appreciate the input.

I’m running on 3 weeks here, for the 2nd time. I was just informed today that my car was driven and issue confirmed. Since this is the 2nd time in so recently for a similar issue, I was told I am getting a full transmission rebuild this time, as opposed to a few solenoids, valve body, fluids, and gaskets. If I’ve learned anything,I’m not too sure these local dealerships ( I live in the largest city in my state) always know everything they are supposed to. I’m not sure if paid dealership work is expedited any quicker in these times but the wait times and games service departments play these days… are really the only problem I have with a Chevy..

[ZLRob]

That's either a bad ring and pinion which has a incorrectly set/ poor contact pattern or a bearing on the diff itself.

I had an old 05 GTO where the thread in style bearing on the IRS diff backed out and continued to back out until it let go. I had no idea what happened because everything appeared intact until the diff was finally removed and on the ground. It had a roaring/ whining issue only at decel as well if I remember correctly. Though it may have been at accel. It happened so long ago that I can't remember anymore. I'm not saying it could be that, but I would be careful with your driving, especially given the sound you are hearing.

[cjperformance]

Originally Posted by ZLRob

That's either a bad ring and pinion which has a incorrectly set/ poor contact pattern or a bearing on the diff itself.

I had an old 05 GTO where the thread in style bearing on the IRS diff backed out and continued to back out until it let go. I had no idea what happened because everything appeared intact until the diff was finally removed and on the ground. It had a roaring/ whining issue only at decel as well if I remember correctly. Though it may have been at accel. It happened so long ago that I can't remember anymore. I'm not saying it could be that, but I would be careful with your driving, especially given the sound you are hearing.

I would agree but he said they replaced the diff. What about halfshafts and wheel bearings? Or even something rubbing the driveshaft, or the DS itself?

[ZLRob]

Originally Posted by cjperformance

I would agree but he said they replaced the diff. What about halfshafts and wheel bearings? Or even something rubbing the driveshaft, or the DS itself?

Halfshafts do not fail in that fashion and since they are incapable of turning in the rear, the only duty they ever see in the rear is torque distribution to the wheels. They are in essence dummie units. Wheel bearings, possibly, but you indicated the noise was specifically coming from the rear end, so my first thought is something in or attached to the rear end.

Driveshaft, possibly, the center carrier bearing is also capable of causing that noise. If you can just lay down behind the car and take a look at things and see if anything looks amiss or out of the ordinary.

The only other thing you can do is take it and have another shop inspect it. Too many possibilities.

[pcelenta33]

Originally Posted by ZLRob

Halfshafts do not fail in that fashion and since they are incapable of turning in the rear, the only duty they ever see in the rear is torque distribution to the wheels. They are in essence dummie units. Wheel bearings, possibly, but you indicated the noise was specifically coming from the rear end, so my first thought is something in or attached to the rear end.

Driveshaft, possibly, the center carrier bearing is also capable of causing that noise. If you can just lay down behind the car and take a look at things and see if anything looks amiss or out of the ordinary.

The only other thing you can do is take it and have another shop inspect it. Too many possibilities.

I appreciate the Input guys. I spoke to the dealer today and they had it hooked up to chassis ears, but they will be removing them and I am picking the car up on Monday. I will probably be taking it to another shop to get a a second pair of eyes on it.

They did mention they changed the wheel bearings as well so that's another item off the list.

Apparently they escalated the issue to chevy engineers and even with their trouble shooting they could not get it figured out. At the same time they also were very confident that this was not a safety issue although it still is a little concerning. I took it to a popular dealer in the Twin Cities area and they have not experienced anything like it to their knowledge, great....

I'll fill yall in when I get the car back.

[ZLRob]

Originally Posted by pcelenta33

I appreciate the Input guys. I spoke to the dealer today and they had it hooked up to chassis ears, but they will be removing them and I am picking the car up on Monday. I will probably be taking it to another shop to get a a second pair of eyes on it.

They did mention they changed the wheel bearings as well so that's another item off the list.

Apparently they escalated the issue to chevy engineers and even with their trouble shooting they could not get it figured out. At the same time they also were very confident that this was not a safety issue although it still is a little concerning. I took it to a popular dealer in the Twin Cities area and they have not experienced anything like it to their knowledge, great....

I'll fill yall in when I get the car back.

If they have not deemed it a safety issue then you need to get that in writing, as any issue which may rear it's ugly head while the car is under your possession after the fact will hinge solely on that invoice they gave you and will or will not be covered or taken care of if you have that or don't. Drive safely and be careful out there if you do take it out.

[NG329]

I vaguely recall seeing a thread on here that said howling could be caused by improper oil in the eDiff.

You might want to get it back from that dealer and take it somewhere else and have them pump out the old eDiff fluid and watch them put the ACDelco stuff in there yourself. I recently did this on my car.

[pcelenta33]

Originally Posted by ZLRob

If they have not deemed it a safety issue then you need to get that in writing, as any issue which may rear it's ugly head while the car is under your possession after the fact will hinge solely on that invoice they gave you and will or will not be covered or taken care of if you have that or don't. Drive safely and be careful out there if you do take it out.

Good looks, I will be sure to get something formal from them before I get it back.

[pcelenta33]

Originally Posted by NG329

I vaguely recall seeing a thread on here that said howling could be caused by improper oil in the eDiff.

You might want to get it back from that dealer and take it somewhere else and have them pump out the old eDiff fluid and watch them put the ACDelco stuff in there yourself. I recently did this on my car.

If you happen to see that thread let me know. I've been searching and can't find anything.

I'll give that fluid change a shot, they told me they changed the diff but honestly who knows I'll try anything at this point.

[NG329]

Originally Posted by pcelenta33

If you happen to see that thread let me know. I've been searching and can't find anything.

I'll give that fluid change a shot, they told me they changed the diff but honestly who knows I'll try anything at this point.

Here's one I came across. A few guys mentioned that the groaning stopped after the fluid change. There's a specific procedure to ensure the correct amount of fluid is in the diff housing. Also, the correct ACDelco fluid has an additive in it.

https://www.camaro6.com/forums/showthread.php?t=535411

[Gunkk]

Originally Posted by NG329

I vaguely recall seeing a thread on here that said howling could be caused by improper oil in the eDiff.

This is correct. If the incorrect oil is added without the friction modifier, it can cause a slip-stick groan in the clutches: https://static.nhtsa.gov/odi/tsbs/20...37572-9999.pdf

Also found a TSB for an incorrectly machined surface of the carrier bearing bore (prior to 2020 MY but you never know): https://static.nhtsa.gov/odi/tsbs/20...72810-9999.pdf


Good luck!