Not likely the motor.
What probably is happening is the plastic slider that attaches the metal window track to the cable has disintegrated. This will cause cable binding problems and unexpected actions with window operation.
The most common problem is that the window will not go all the way up. Gravity overcomes the problem with the window going down, but it's a jerky motion at best.
The rear window mechanisms have this plague...the front ones are an entirely different setup.
This is a DIY fix, but door panel removal is a requirement.
At best, if you haven't been playing with the windows much, the plastic pieces can be had for about $2 apiece. Otherwise, (as in my cases), the cable is pretty buggered up, and the entire assembly has to be replaced ($140 apiece).
Reply if you need more info...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car