Have you tried pulling the belt off, and running the vehicle without the belt (just for a minute!) to be sure that it's a belt driven accessory? if the noise goes away with the belt off, then it most likely is. Then, with the belt still off, you need to turn each pulley and see any of them have loose bearings or don't feel smooth when you turn them. Also, check your fan clutch for looseness, and check your water pump for leakage.
Just some ideas before you spend any money...you may be able to fix it yourself quickly and easily!