2000 Honda CRV noise on start up

Noises problem
2000 Honda CRV All Wheel Drive 90000 miles

When I start my car it makes a squealing sound. If I rev my engine while still parked it goes away within a few seconds. This happens most often if I haven't used my car for awhile. If I make a short stop somewhere and start my vehicle up again it doesn't last very long. The dealer told me last year that it was a b/c of a worn fan belt and they replaced it. After a few days (not more than a week) the sound came back. Could this be the tensioner? I'm taking my car in in a few weeks and would like to know if they can fix that if that is the problem.