Could a weak fuel pump cause fuel starvation to the point where the car actually vibrates when trying to accelerate? This has occurred sporadically when accelerating from 2000 rpm at 35-40 mph or so. I've assumed that the driveline was somehow out of balance. The fuel pump has been making a much more noticeable "whirring" noise when listening to it from outside at the right rear of the car. I listened to another c280 i have access to side by side and the fuel pump very quiet and hardly discernable. Impending pump doom and stranding? Of course, I will try to get it to my mechanic as soon as possible.

P.S. I switched out the fuel pressure regulator between the 2 cars and not much difference in my car, and none in the other.