Sounds to me like a bad bearing in the compressor clutch hub, are you sure it spins smooth? Does it spin totally free with no rough spots?
I have some other theories, based on the idea the vibration your seeing in the belt tensioner is normal. That “ball bearing in a can” sound from that part of the car typically means one thing. You have something stuck in and bouncing around your vent fan blower. Just turn off your vent fan and recheck for the noise. Another theory is, it might be one of your radiator fans. Be aware the one behind your A/C condenser will always start when you turn on the A/C. Another easy thing to check.
I’ll be around most of the day if I can help more. Good Luck
