Clean it out.
Look for broken squirrel cages.

MONO BLADE VERTICAL parked windshield wiper
http://members.lycos.nl/mbenz/windshield_wiper.htm

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=201028%5F15C&M=102%2E985&GA=722%2E408&GM=717%2E412413&CT=F&cat=15C&SID=83&SGR=060&SGN=02

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=201028%5F15C&M=102%2E985&GA=722%2E408&GM=717%2E412413&CT=F&cat=15C&SID=83&SGR=045&SGN=01