I had originally thought that the oulsing was caused by sticking calipers but have thrown that out the window. It happens when i am trying to keep at a constant speed (light throttle). It goes away after put my foot down harder onto the pedal. The RPM will do a little dance when it starts to happen, it was only happening at 20 to 35 mph but has started to do it at around 40 to 45. Also what size are the speakers in the rear and on the front doors? lol