I have seen this issue quite a few times and almost everytime it was grease in the solenoid or on the helix on the drive pinion, both cause this behaviour, a good cleaning takes care of this.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)