Started making a screeching noise

If the belts from either the alternator or the serptine get any oil or grease on them, that would cause them to slip causing the screeching noise. Also if any water gets on them the same would occur, have you heard it when the outside temp. Changed. The reason is that I did my belts and the tensioner pulley(not the tensioner) and I hear the same noise during an initial startup, but out goes away right after it occurs(MOISTURE is the culprit).

I took it to the local dealer as I was having AC problems along with the squeal they told me that I needed to replace the front fan, etc. $700.00 later. They said that my belt was loose and that a retaining/set bolt was missing and the part would have to be replaced at sometime, but they tightened it up and it should be good for awhile. I asked them if it should be replaced right away and they did not seem too concerned that I would have any problems. I have noticed the squeal when the moisture seems to be higher and when it cools off in the evening, Yesterday the belt went out so it is going into the shop for a belt replacement. I wish they would have repaired the car completely the first time I had it in, replaced belt and missing bolt part, instead of calling it an old school fix and I would not be out the expense of a second car rental. I had asked them to replace the belt when I first brought it in and they said it didn't need it.