My car started making this weird sound over the weekend in spirit of 4th of July I guess. It is only when I deaccelerate and let of the gas at low speeds.

It sounds like a loud banging from the rear of the vehicle behind the transmission. At first I was thinking it was the Axle, or rear differential. I peeked under the car and everything looks to be in order no leaks and everything seems attached. I wish I had a GOPRO I could stick under there to pinpoint exactly where its coming from. If I accelerate it goes away completely. My thoughts right now are that it might be the driveshaft related or a rear bushing that may need to be replaced. Help me pinpoint the issue.

Listen carefully to the attached video. Listen at 3-10 seconds approximately. Its almost like a banging sound when I deaccelerate. Rear is all stock at the moment 3.42 gears m6 Formula LS1.

It will also not make the sound if the car is stationary with a rev or if I accelerate. It only makes the sound when deaccelerating at a low speed coming to a stop.

 

I couldn’t get the video to play but have you looked at the torque arm bushing on the transmission end? I recently replaced mine because it was “chewed up” and when I’d brake the torque arm would bang around and make a knocking sound.

 

I couldn’t get the video to play either but ujoints on ur driveshaft can cause a similar noise.

 

It could be possible to be the u-joints but my money would be on the ring and pinion. Remove the diff cover and look at the teeth. Bearings might be worn allowing the gear mesh to change when unloaded. Sounds loke there are a few damaged.

 

It bangs when he decelerates. Gears don’t “bang” really. When my torque arm bushing was bad there would be a knock, knock, knock (bang, bang, bang) when braking at slow speed. If the gears were bad enough to make a “bang sound” I don’t think it be driving anymore after the bang. “Gear noise” is usually more of a grinding or whining sound.

 

Alright well I took it to the mechanic this morning. He checked the differential and said the good news its NOT the differential, transmission, driveshaft or u joint. (deep breath) I uploaded the video to YouTube so you can hear it.


He advised that the rear tire assembly looked to be really damaged on both sides and looked as if someone attempted to try to steal the rear rims off the car and did some damage in the process. I have wheel locks on the rims which may have saved it or at least slowed someone down if that was the case. I do park on the street and who knows NYC isn't always the best place to park. There's been a string of thefts for catalytic converters around my neighborhood lately so who knows. The mechanic said the torque arm and bushing looked to be in real bad shape as if someone tried physically breaking it. He stated it looked so bad that it was possible that the rear wheel could have popped off and I was lucky to come in when I did. He is redoing both sides to be as good as new with a $700 price tag with labor included. I will put the itemized parts list on when I pick up the car tomorrow. Still cheaper than rear replacement.

This was still a learning lesson though and my 98 is getting older. I purchased new gaskets and will be changing the differential fluid next week with some fresh Royal Purple and additive. I am also looking to purchase a LPW- 10 Bolt w/ Brace Kit for that additional insurance on the rear for the future.

 

He’s changing both sides of what? knocking/banging is definitely the torque arm bushing on the transmission. The bushing on mine as destroyed by transmission fluid leaking on it out of the transmission tail shaft. . But yeah the knocking is going to be the TQ arm bushing, not the wheels.

 

So the mechanic didn't put new fluid in the diff when he checked it? Or you just want Royal Purple?

 

I agree the banging could have been the bushing on the tranny partly causing the noise but may not have been the whole story. He actually said the Trans mount looked worn and asked if I wanted to replace that also but after paying $700 I might wait on that. He wanted like $295 and if its just the bushing its like $30 so I figured I can look into doing that myself or at another shop. It seem solid enough when driving I don't have any play right now when going through the gears so we shall see. Not sure if the mechanic put any fluid when he checked the differential because it wasn't listed on the receipt. He did say it wasn't the issue of the noise.

I plan on replacing rear diff fluid in the near future anyway and wanted to upgrade to the LPW Brace kit so figured I'd use the Royal Purple based on feedback. Figured it would good to strengthen the rear for some insurance and peace of mind.

Here is a list of the parts, it's the labor that was expensive.

Parts:
Left and Right Rear Axle bearings
Left and Right Studs and Lug nuts
Parts=$244.95
Labor= $495

It seems to be driving smoothly and quietly no more banging. To be honest the car sounds completely silent now except for my exhaust not even a rattle. I can now enjoy my exhaust notes again.