Steering Wheel - noise when released

I hadn't driven the car for a couple of weeks. The steering wheel was set in it's upper rest position. As the wheel was programmed to be lowered, when starting the car the wheel made a 'thunk' before moving to the pre-set position. The noise was almost like it hadn't released from some other part.

As I was heading to the dealer that day for an oil change before the car gets bedded down for the winter I told the AMG Service Rep. Picking up the car they said that they couldn't replicate the 'thunk' but serviced the steering parts anyway. Although there was a slight 'thunk' when I picked it up it certainly wasn't the same noise.

Yesterday having left the car for a few days, the weather was mild I thought I'd take the car for spin....you guessed it a 'heavy' thunk as the steering wheel was released............I have told the dealer (the car is still under warranty). We have had 6 Mercs in the family previously including my R171 and have never had this problem.

Anyone else experienced this or have an idea what could cause this?

Thanks