thank you!x2, could be the idler. It's fairly easy to take off the belt, and if it's in good working order, it will save you $12 +. The alternator belt has come off first, search and you'll find lots of video and writeups about getting it off. It's a simple job - almost exactly the same method to removing the A/C belt.
Once it's off you can spin the idler to see if it's loose or chattering - which would indicate it's making the noise. The A/C just might be low on freon, adding to the misdiagnosis. Better to get a set of gauges on it to determine what's really wrong rather than make expensive decisions based on something making a noise.
It could be the alternator. Front accessory drive noises are hard to pinpoint.
One method is to use a mechanic's stethoscope - a long rod that is hooked to earpieces so you can literally hear which bearing or area the noise is coming from. A good substitute is a long screwdriver, place the tip against that part while the engine is running and listen with the handle pressed to an ear.
Caution: The engine is running, the belts are turning, it's not a casual job.
Don't cut the belt. You may very well find out all you did is spend money to replace something that is making the noise, plus a good belt too.