Belt Squeal
 

What causes that infernal squeal when I start my truck? Are the belts too tight?

if anything prolly too loose but if youve recently replaced a squeaky belt its possible that one of the pulleys is a bit polished and mirror finished so that it allows the new belt to slip you need to change the belt to a new one if ya havent already and use some real fine emery cloth or something to scuff up the pulleys to allow the belt to grip better and you should be fine.. also make sure everything is lined up nicey nicey too

at start up it is likely the alternator belt. if your battery is aged then it is being strained at start up and the alternator is going allout to charge it / it is having a full load on it, so that belt squeals. kinda like when you leave your lights on and your battery is drained, the belt squeals like a bia. Thats my guess.

if the belt is shiny than you should replace it. a loose belt is bad but you can also overtighten.