I have a 1988 ford f-150 and there is a very loud squeaking noise on in the morning when I first start it up or on day that are very foggy or raining. I was thinking it was the belt but the tension is corrct to the book. What else could it be? a pulley? Please help me it is gettin very annoyying.

 

Look closely at each pulley - one may not be turning. It could still be the belt if it's heavily glazed. Try some "belt dressing" available at most parts stores. The tensioner pulley often goes out - use a piece of hose as a stethoscope to pinpoint the noise.

 

When it starts and is makin racket spray some wd 40 on the tensioner and see if the noise stops. If it does think about replacing the tensioner.

 

Check your fan clutch, too. When you turn your engine off, does the squeaking continue for a split second?

Andy