Rear End Metallic Noise
 

I tie-wrapped a microphone under the rear of the car to record this noise. I uploaded the wav file to a hosting site as this site doesn't accept audio files. Hopefully the link will work. The noise only occurs after driving 15 - 25 miles. Luckily the noise occurred at a location where I could avoid traffic. Unfortunately the reason there was no traffic was because the road was covered with gravel for repairs. So ignore the road noise, but you will hear a metallic noise like dragging tin cans. As I accelerate, the noise goes faster. I called my mechanic on my cell phone so he could listen to the noise. He couldn't diagnose the cause in that manner, but said come right in so he could look at it. Since there was little traffic I decided to try going in reverse even accelerating in reverse: no metallic noise. Now no noise going forward! Going in reverse temporarily cured the problem. Is that some sort of clue? Drove the 20 miles to the mechanic and the noise wouldn't come back so didn't bother him. Hopefully I can repeat tomorrow with better luck, but would certainly appreciate any comments. mb1985rearendnoise300dt.wav - 0.33MB

Well, noise from the rear is never good, It could be something simple like brake pads, or your parking brake pads, and driving in reverse could have helped.

It could be bad rear wheel bearing, or bad rear axel (CV shaft) or differential.

Im betting on parking brake pads and rust...

My strong bet is on CV Joint. Sounds exactly like the noise my 300E made. It increases in frequency with the speed of the car. The other big clue is that reverse will stop the noise. This is a well known trick with bad CV Joint.

If you look around the rubber boot, it will probably be split and greasy. Mine made noise only in cold weather and went away after several miles. Then it got worse and finally, one fine day close to home on a city street, it started an ungodly screeching. Made it home at 10 mph, replaced the axle with a new one and problem solved.

Steve

CV Joints
 

Thanks softconsult and Icefire. You both mentioned CV joint. Today luck was on my side (well lucky finding the problem :) , but not so lucky finding out that the problem is the CV joint:o ). Drove out 10 miles then headed back 10 miles to my mechanic and the noise started just 1 block from his shop ;) Mechanic says CV Joints. Lots of threads recommend CVJ reman half axles. Mechanic said buy them and he'll put them in. Just did: $142 + $50 core each + shipping ($20 total shipping estimate).

eesh that sounded worse than mine..mine was just a bit quieter..but thats the sound...got the car up in the air..and sure enough there was a tear in the boot..it was in a position in the boot so unless u really looked for it you wouldnt see it..but it was all outta grease..

it is rare that both sides would fail at once.

this is not a part that i would replace preemptively.

tom w

...unless like me you decided to spray some protector on the rubber when you got the car, which opened up cracks in both CV boots.

Not the best move.