Sometimes squeaky belts

[sting2k7]

Hi guys, I just got a used 2006 mazda 6, it has 52k miles on it. I really like it and it is in excellent shape.

I have had it about 2 weeks now and one thing I noticed is that sometimes when I start up the car there is a pretty loud constant squeaking. I have looked and it is coming from one of the fan belts. But it doesn't do it all the time, normally only in the morning after sitting cold all night and the squeak begins to dissappear within 5-10 mins of driving around. Other times it doesn't do it at all, during the day I never normally hear it or it is much quieter. I took it back to the dealer to see what they said, of course it didn't squeak for them but they checked the belts and pullies and claimed they were fine. Has anyone had this happen. I am supposed to make arrangements with the dealer again to leave it over night so they can let it sit and start it up in the cold which is when it normally happens. Thanks for any help.

Also the car seems perfectly fine, there are no studders when accelerating and everything operates normally. Just the squeaking belts on start up sometimes.