I had a similar sound. The culprit turned out to be the rubber molding around the base of the wiper arm (driver's side). The molding was slightly ajar and interfered with the rotation of the wiper arm causing the squeaking/grinding type noise. I opened the hood, realigned the molding, and haven't heard the sound since.
Squeaking wipers/Wiper noise?
Has anyone experienced a very low squeaking sound, on the upswing of their front wipers? I hate to even call it a squeaking because it really isn't....It sounds more like a spring being stretched. I just picked up my car on Friday and today, I had to use the wipers for the first time. Just curious...... 
