2006 Mazda 3 squealing on excelleration, could be a belt?

I've had this strange noise from my car for almost a year now, but every mazda dealer I take it too, they say its fine.
when my foot is on the gas and I reach 60-80km and the car stops excellerating and levels out a squealing noise is heard inside the car, once I take my foot of the gas the noise stops and once my speed is high enough, like over 80km/h the noise stops. It is very strange but it is bothersome, I was hoping you could help me out a little b/c its a fairly new car and its in good shape. Thanks

chris.