I have a 1995 f150 302, pollution pulley was thought to be cause of sqeauk but when bypassed with new belt, still have a bad squeal when I start up and sometimes quiets down after driving awhile, have new idler and tensioner pulleys ! What's wrong?!

 

No tellin. Do you see vibration up and down or side to side? If you have a AC does the pitch change when you engage or disengage the AC? Has it been dry or muddy there? You can spray the belts down with a little water then crak it to see if it stops. If its still squalling you can remove the belt and hand feel the in and out play and any wobble on each pully. the Vacuum pump normally has a tad of in and out play. Mine was doing that and come to find out that the belt that was given was for a IDI truck so it was ever so slightly wider. Very little. I alos find that some harmonic ballancers have one ridge more than is required for the belt to ride in. If that is the case make sure the belt is riding close to the engine on the pully and not the outter edge.

 

I can't notice any vibration but, when I chane ac off it does change sound tone

 

That could ne nothing. But then it could be your ac bearings or the clutch pully