I recently changed out my original runflats for non-runflats (Pirelli) and had the wheels balanced and front end aligned at the same time. I'm now experiencing an occasional rhythmic vibration (not a shimmy) from at least one of the wheels when accelerating on smooth pavement. This only happens some of the time, and stops when I let off the gas. I've had the car into my dealer (where I bought the tires), who was unable to replicate the problem (not surprising since it only happens occasionally) but rechecked the wheel balance and alignment. This problem seems to manifest itself more in mild weather than cold, but I could be imagining that -- the occurances are so erratic I can't detect any pattern.

Any ideas?