Sounds like your bearings are dry, if the fan was removed and turned upside down and the tinyest squirt of WD40 was put on the bearings without going all over the coil, I found this solved it for my ultimate, Heres the snag you have to be CORGI registered and it will cost you approx 120.00 plus fitting, and it could possibly be solved with a squirt of oil.
CJ, June 2008