Hi! I'd like to put in my 2 cents worth on this. From what you described as the screeching noise at 5K RPM, I'd suspect that the serpentine belt was slipping. Probably wouldn't hurt to replace that. Of course, it could have been squeeking because the idler pulley was binding. Sometimes the balls inside the bearings develop minute flat spots on them. Occasionally, they shift so the flat spots are rotating within the race, hence the whirring noise. The bearing also binds slightly because of this. They usually rotate back to their normal orientation and the noise stops. Maybe this is what's causing your problem. Just my opinion though......
