I just purchased another e30, this one a 4 door, and this one the passenger window is really loud when it's going down, and really slow and loud when going back up. Is this the regulator? or is there something else I should look at. The passenger rear window doesn't work at all. I haven't tried swapping the switches, and that's not a huge concern to me, but I'm not sure if the 2 issues are related.