I just bought an '83 300D AT 172k .

Where to begin! So far I really enjoy the car. It rides well on the highway for a 30 year old car, and the new tires have helped with that. The entire 'air filter assembly' has been removed in favor of a cone-style filter mounted to the front of the turbo; a temporary solution for now. Blow-by is captured by a makeshift series of lines. I mention that as it *could* factor in, but that is unlikely.

I have put about 1,200 miles on the car. I've noticed that there is a vibration that I cannot diagnose, and I've done some research here on the forum and have not found what I think to be a description of the noise.

The noise 'sounds like' a wheel bearing/hub might sound, but is unrelated as it continues to some degree even with the car at idle.

To me, it seems like a 'harmonic balancer' type of sound, like one of the accessories has bad bearings, or perhaps something even more nefarious located inside the block like the crank or something.

To some extent, the 'waves' of the vibration get closer together as RPMs increase, but they never really become any closer than about 1 second apart.

My attempt at onomatopoeia is: wob [one second] wob [one second] wob...etc. It's a very 'deep' sound and as I'm driving down the highway at ~65 mph, if I lean close to the windshield I can hear the sound much better (resonating off the inside of the windshield?).

Any guesses as to what this could be? I thought perhaps it was related to the driveshaft/flex discs/centering cone/etc. but it continues to some extent while at idle, as I mentioned above.

Thanks all and I look forward to interacting with you as I go through this car and fix/upgrade/maintain it!

JD