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.