Only just spotted this - sounds exactly like the problem I had that was failed spot welds at the bottom of the A pillar. First on the OS and then the NS! It took them 4 attempts (I think) to fix the OS, that included fully removing the dash and windscreen (I believe they managed to break 2 screens doing it!). They had 2 goes at the NS and whilst I didn't think they fixed it at first it seems to have gone.
It is fixable and it is a known problem to BMW - keep on at them if they aren't forthcoming at first. However, don't expect your dash to be creak/rattle free when you get it back!!!!
320d M Sport (E90)
Le Mans Blue/18" Alloys/Bi Xenons/Climate Screen/Black, Heated Dakota Leather/6 CD Changer with Dension 500/Power Mirrors/M3 Lip Spoiler/Gloss Black Grills/Through Load, Storage pack, Lumbar Support, Smokers Deletion