Ford Repair: 98 Mustang Squealing Noise, crank shaft, belt pulley

Question
Recently my mustang has begun to squeal on cold start - I have replaced serpentine belt, and water pump, tightened crank shaft pulley bolts and still no luck -- I did apply stp oil treatment and that made it quieter but not completely gone - I do know that some o2 sensors need replacing and am wondering if that could contribute to squealing noise; I have run the car without serpentine belt and noise has persisted - belt is not the issue from what I can tell; I'm at a loss - car is now at 125,000 miles - hope this is enough info to give you some idea of what's happening - Thanks


Answer
I have not seen a squealing noise from an engine that was not releated to the belt/pulley system.  A bad O2 sensor(s) could not cause a squealing noise.  I would try removing the belt again, and listening to the engine with a automotive stethoscope.  Being that the noise happens so often, it should be fairly easy to pinpoint.

I hope this helps,
Dave