loud rear wiper motor

Ok I have a 97 with a rear widow wiper that in the last couple of years has started to make an awful "whirring" noise when it wipes back and forth. If functions perfectly fine and doesn't seem to be getting hung up or anything just makes a loud noise clearly heard over low music and road noise from my 33 KM2s. I am thinking is is just an old wore out motor but thought I would post up and see what someone else thought or if someone has had this problem and how they fixed it? I plan on getting the parts from my local pull-a-part so I wanted a plan of attack so I wouldn't buy more than I have to.