Hello out there!

My sliding roof quit working. I had it repaired a little over a year ago and it cost me a fortune. They had to replace the arms. But it worked fine until about a week ago. When I push the switch, I can hear like a sucking sound from the drivers side rear. The roof seems to try and move but just can't. So it sounds to me like the electrical is ok. Any thoughts as to what this may be?

Thanks

1990 420 SEL