w210 possessed rear window
 

It think this may be the first symptom of the rear window regulator problem, but I thought I would ask:

Today, while on the phone and idling in a hospital parking garage as is one of my daily customs, I thought for sure a friend was playing tricks on me. I swear someone was knocking on the rear passenger door and hiding. Closer inspection revealed that there was nobody there... and I was in fact not going crazy.

As it turns out, the rear window regulator was going on and off all on it's own. I lowered the window all the way then watched it go on and off spastically until the window reached the top. At that time I heard the same noise I did origionally...the window motor going on and off while the window was wlready up.

This sure seems like an effective way to quickly burn up a motor. I am imagining there is a lose wire/contact somewhere. Does anyone know where? Is there any way to salvage the motor now before it burns out?

Our 1998 E300 had the driver's rear window fail, but it did not do as you describe. It failed to operate, and many bits were replaced in an effort to make it run properly. I have heard of "gremlin's operating my window" from other W210 owners. On my car they ended up replacing most of the window mechanism as each time I got the car back, a different part would fail. It also went out of synch all the time too.

We commonly see window switch assy cause this. It does this after a spill or good cleaning of the center wood.

Replace the switches. It sounds like it may have killed the window regulator. This is a little tough to change because it is riveted to the door frame.