It's a pain in the arse to get to it, door card off, window out, window winder mechanism off, then you need an m8 spline/triple square bit to take the door module out, don't use a torq bit as you will round off the screws! When you finally get the door module apart and split, inspect all the soldered joints, re solder any that look dodgy. There should be a DIY for this somewhere on the forum.