No direct experience with the V40 but had a similar problem with our Miata. I used white lithium grease in a spray can with one of the plastic strays to spray grease into the window tracks inside the door. You can move the weather stip just enough to get the stray inside and into the track. Others had success on the Miata with removing the door panels and using silicone grease. The lithium method is not a perfect solution since you can only lubricate the top part of the track without removing the door panels, but it stopped the squeaking and it moves easily now. Don't spray grease on the windows or you will have a real clean up mess.