Engine vibration at 3000 rpm - 190E

My 93 190E 2.3 auto has around 127K miles on it. I've been puzzled lately as to why it has developed a high frequency "trembling" feel, felt through the steering wheel, the seat, and even the accelerator pedal. Sitting still, if I rev it up to 3000+ rpm, I feel the same thing. The idle is stable (not missing), but rougher than I think it should be. Engine mounts were replaced 8,000 miles ago.

Is this the sign (or imminent) of a blown valve? bad compression in cylinder? fouled sparkplug? some bearing? Or just a fact of life with a largish, old, 4 cylinder?