squealing noise

There is a high pitched squealing noise coming from the under the hood. i just replaced all three of the drive belts. the noise only happened once. any ideas of why it made that noise would be appreciated.

1996 Mitsubishi eclipse gsx
76500 miles

belt is too loose....I would tighted it up if it continues...mine would do it until it warmed up a little bit...I went through like 3 belts in a month because I thought I had it tight enough but I was wrong....

If it only happened once, then it's no longer a problem...