Had the same screeching situation. The noise would subside after a while but it kept getting longer before it would quiet down. Test the fan motor by pulling the red positive lead from the relay and the black ground wire as well. Connect these leads to a 12V source and see what gives. Try the oil fix if you can get to the shaft bearings. They are pretty well buried. I bought a fresh motor from an eBay vendor and replaced old (13 yrs) screechy. All is quiet now. FWIW, I really doubt the electrical connection explanation would cause the motor noise.
