I would run it for a couple of hours with music into a dummy load to confirm that it's OK. It doesn't have to be at full power for this although I would test with the amp driven to intermittent clipping with music before calling it repaired.
Think the sound coming from the board itself is normal? I've heard of that happening but it was new to me. What components would that be from?
It's more common to be coming from wound (inductors, transformers) components than the semiconductors or resistors (although the resistors are wound, but bound to a ceramic core).
Wearing a new pair of latex/nitrile cloves (not conduction), touch various components to see if touching anything quiets the sound.
Wearing a new pair of latex/nitrile cloves (not conduction), touch various components to see if touching anything quiets the sound.