JKehler

Okay, guys. Here is a real head scratcher. At highway speeds, namely, 75 miles per hour and above, I get a knocking sound from the left rear that sounds like rocks or stones hitting the fender inner liners. It does not happen at speeds below 70, does not change frequency with speed, and is not influenced by the road surface or braking or turning.

I don't get it. I can drive 65 mph on any road surface for 100 miles and hear nothing. I drive 1 mile at 85 mph on a perfectly smooth road and it sounds as though the left rear tire is picking up rocks and hurling them into the whee arch.

Anybody have a suggestion where to look? I have heard everything from a bad shock damper to sway bar end links to sway bar bushings. I have inspected, pried on, and torqued them all. The noise persists.

Any suggestion would be greatly appreciated.

JKehler

Okay, guys. I am going to answer my own question. My knocking sound was actually a loose trim strip. It is the black trip strip that goes from the base of the windshield on the driver's side, up over the roof, and terminates at the rear window. It is located in what we old geezers refer to as the drip rail. When SafeLite replaced my windshield a year ago, they re-used the plastic clips that hold the trim piece on. Every once in awhile it pops up. That was what was producing the noise at speed. This probably won't be your solution if you have this problem, but it goes to show, you have to look at everything. Noises are tricky, they can emanate from the darnedest places.

RedGray

I'm glad that you found the problem!


Btw, my guess is that if you went 140mph, the rate of the knocking noise would be different.

But officer, I was trying to get a better idea of what might be causing the knocking noise in the back.

kasparovitch

JKehler, can you offer pictures of the location of your problem?

I have a W202 with mysterious rear noises like chunks when driving only and only when the surface is irregular, like passing holes, for 10 years and almost every detail in suspension has been checked or replaced without any help.

So I'm very interested in alternate hypothesis, as yours. I suspect that this can be caused by torsion of the car metallic body.

Thanks.