Why does the wheel rotate on its own without being driven?

wheel_share.zip (884.6 KB)

I imported a wheel assembly and a purple object from CAD. The wheel is attached to the purple object using a rotary joint. Even though I only set the joint friction to 0.01, it rotates by itself. When I set the damping value in the drive to 1000 and the speed to 0, it still rotates on its own instead of following the speed I set. What could be the reason for this?

friction