My 1997 850 had this problem. It turned out to be the bearings in the white metal bracket that supports the wiper system. Spray some WD40 on the base of each wiper, make sure it gets past the plastic cover under the wiper arm. If this solves your problem you need to completely disassemble the wipers then lube and ream the bushings for each wiper arm. This is big job (took me about three hours) and is the result of poor design. The wiper arms have no grease grooves and the white metal bracket seems to contribute to the problem because the bushing in the bracket is too short. Mine failed in a major snow storm, don't wait for this to happen to you. I hope you don't ahve the same problem, but if you do get it fixed now.