New owner - 2007 e4 - surge at constant speed

Car has ride 4 fun motor and new gel batteries. Gearbox seems to be a little noisy and regenerative braking causes a high pinched squeal, but the most significant issue is a rhythmic surge when holding a constant speed. Cannot feel a surge during acceleration. Any guesses as to where to look first. Accelerator switch?, controller?, bearings? Constant velocity joints? Any help would be greatly appreciated.