Noise when opening trunk

Dear friends,

I went to a premium bodyshop for painting the back wing of my X6
(to remove a small bump left by someone opening a door on a parking lot )
When I got the car back.. everything was nicely painted of course and the small bump removed..
.. now when I open the boot lid (I took the option of having it open/closed with the press of a button) it makes a strange noise.. sometimes it doesn't open all the way anymore..

The bodyshop is questioning if I already had the problem before.. which was not the case!

Anyone an idea what the problem could be ??
.. how this can be solved ?