Nice going. I would say that if the noise goes away when the ac is on, you have found your problem. That's not 100%, since the added load on the belt by the ac compressor could be changing the dynamic for other parts. The clincher is being able to locate the noise as being in the compressor clutch area.
When the clutch is engaged, the entire assembly rotates as a unit, and both the inner and outer races of the bearing move at the same speed.
Make sure you compare your assembly with the replacment. You want to have the part with the bearing (there are several clutch parts available) so make certain you have what you need before you leave the store.
As for doing the job, be very careful. You will need to either do this job from below or above, but either way you may have to remove the bolts that hold the compressor to its bracket. Be carful to not put a lot of exrtra stress on the hoses by twisting or dangling the compressor by the hoses. So, support the weight of the compressor to take the weight load off the hoses. If you have room, do it with the compressor in place. Not very comfy, but it's better to not disturb old hoses.
Wear safety glassses or a clear face shield in case the refrigerant escapes. At minimum, you could get a freeze burn on your skin, but it can be much more serious, such as a frozen eyeball, inhalation injury, or even the creation of poisonous phosgene gas if there is a flame nearby. No lanterns that have a flame, or even garage furnaces running!
Finally, make sure you have the right air gap at the clutch magnet. Unless the parts man can tell you it is correct from the factory, check it with a feeler gauge and adjust it using shims. If you don't have a feeler gauge, you can estimate the gap using an object that fits the gap on the old clutch, and adjust it until it is correct.