The car is a '81 300SD

Whenever I run over a small bump or rough road I get a rumbling, low pitched rattle from the front right side. At first I thought it might be coming from the back, and checked the sway bar links, but they're good. My guess is either upper control arm or strut rod bushing. I checked both, and the upper control arm looks like it could be original, and I didn't get any play when I pulled on the strut arm. I put Bilstien comforts on the front about 3 months ago. The exhaust system is tight.
One interesting thing happened this evening when I checked the front wheel. When I bounced really hard on the front right fender, a loud click came from the wheel, I then jacked up the wheel, spun it a few times, checked for excessive play in the bearings and put the car back on the ground. Then when i bounced on the fender again, no clicking noise. Any guesses? Thanks

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'81 300SD