I appreciate the feedback. It's bound to be hard to diagnose just from the video-audio, especially with these motors, because they are a little bit noisy and clackity-clack, sort of counterintuitive given how long they last.

I am halfway through a 2000 mile trip - Bay Area to N. Eastern WA. A few days ago, while I was checking the tranny fluid level, engine running of course, I noticed that the noise had pretty much subsided, that it was sounding like it normally had.

Then it dawned on me, it had made that noise about a year ago after a repair on the air filter mount. I hate to admit that I can't remember what part of that had broken, but I was getting some loud clunking at various points on the power curve, I thought the motor mounts were in serious trouble. One had obvious damage so I replaced them, but that wasn't it. I noticed during all of this that the air filter housing was loose and bouncing at times.

I secured all of that and used those rubber mount bushings, bolt threads coming off of each side of a rubber center part.

It made the same noise. Sort of like a guitar magnifying the sound of that vibrating string, the air filter and housing acted like a soundboard that the engine was vibrating. But then the noise went away, so I forgot about it, but I think for some reason it started making the noise again, and I couldn't figure out where it was coming from.

When I noticed the noise had gone, I also saw that the big wingnut holding the air cleaner housing onto that center bolt was missing. It still had the spring loaded clips holding the lid down, so the air filter still had integrity. Perhaps the wingnut vibrated off and left the whole thing relaxed enough so that funky noise stopped.

This engine can be mysterious. It's running really strong although at times it will act sluggish and weak. And then recover. I don't quite get it.

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1986 300SDL, 362K
1984 300D, 138K