This comment falls into the category of the blind leading the blind so......

My first guess would have been wheel bearing, but you said that it has been happening for the last 4 years.

My second guess would have been brakes, but you indicated that it happens regardless of braking and again for the last 4 years.

My third guess is the rear springs and shocks. If it is still under warranty push for them to replace the springs and shocks with the new updated version.