i had this same problem but my noise was a bit different, was more of a chirping noise. i don't think its the serp belt.
my issue was the alternator, which had to be changed. cost was about $250 for the part, but the labour is brutal, about $600 worth of labour...
you can try to spray the belt with belt dressing (not wd40) and see if that helps
Also, can you go into your car, listen to the noise and once you hear it, turn the Air conditioner on and keep listening then turn the air conditioner off and keep listening, does it go away when a/c is off?