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[pcmaher]

OK, I've read every thread I can find concerning thumping from the rear of a W140. I haven't found a posting with exactly my situation, but some are close. Here goes. My son heard a very slight thumping in the back while the car was moving a couple weeks ago. I hadn't noticed the thumping before because it was so quiet. Now that I'm aware of it, I hear it while driving along smooth sections of road. I don't hear it going over bumps. I hear it better at slow speeds, as low as 5 mph. It almost sounds like something is loose back there in the trunk. I pulled the trunk lining out and looked around. I found a rats-nest of wiring for some Godzilla sound / video system that a previous owner had installed . Some of the wires were heavy gage, and looked like they might be knocking around. So I pulled all that wiring out. I also found a module housing that had broken away from it's mounting tabs, and it was hanging loose against the quarter panel. That could easily have made a thumping noise, so I re-mounted it using some good tape. I took it out for a drive, and within 20 feet I could tell the thumping was still there. I turned the steering wheel rapidly to the left, then right, and repeated this to get the car to bank back and forth to see if the thumping got worse. It didn't, and in fact I couldn't hear it at all while doing this. If it was the top shock bushing, wouldn't I hear the thumping while doing this? I jacked the car up, pulled off the wheel, and looked at every bushing down there (except the top shock bushing...can't see that one). They all look good and there is no play in any of them. I tried yanking on and moving the shock, and felt no play. I jacked under the rear control arm to compress the spring and shock somewhat, and still felt no play. I suspect that the shock is still pressurized though, and that may eliminate any play that may be present. I put the wheel back on, lowered the car, and pushed down on the rear corner. I sometimes hear a creak. Not always. I wonder if this could be what I'm hearing. What could be creaking back there? Is it a bushing? What do you all think this could be?

p.s. I changed the nitrogen spheres (accumulators) last year.