what you are hearing are the teeth skipping on the regulator, it will only get worse, you need to replace the regulator and possibly the motor, not a difficult job if you take your time, expect to pay about $125 or so for a regulator, be sure to lube up everything when putting back together.

__________________
Jerry

2004 SL500 Black 55K Miles
2002 s500 Black 90K Miles
1986 300E Gold 233K Miles
1966 Twin Cessna 320D
1989 Jeep Cherokee 233K Miles
1994 Ford Van E150 399K Miles