I have 2 E46 BMWs, a 325XiT with 131k and a 325Ci with 71k. Both do identically the same thing. One can drive through all speeds 0-100 mph with perfect smoothness. Intermittently between 60-80 mph there is an out of balance sensation from the rear (it does not transmit through the steering wheel). I have both summer and winter tires on both with dedicated wheels. The summer tires are on factory alloy wheels, the winter tires are on aftermarket alloy wheels. The situation happens with both cars and both wheel sets. Tires and wheels are in good balance. Both my factory authorized dealer and my local independent BMW expert cannot find anything. The problem is independent of any condition I can think of and intermittent. I had a similar situation with a 635CSi but it was tire related. This cannot be since it involves 4 different sets of tires. Any ideas? Peter Sexton
sounds like a caliper starting to seize, I've had that exact symptom on two of my cars, and as a tech, saw that complaint on a regular basis, usually confirmed by a wheel that wouldn't spin by hand on the lift and repaired by caliper replacement
