Welcome, I am Chris (aka-Moose)
Can you remove the belt and run it briefly like less than 4 minutes to see if the noise is still there or gone. Gone means its a pulley or pulley bearing with the issue. If its still there, then listen to the bell housing area. The transmission in neutral or the clutch pressed makes me think to check the clutch release bearing and the pilot bearing possibly gone dry and faulty.
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