Chosen Solution
‘‘Note: I did review the answers at iMac has a buzzing noise on the top back left corner My iMac was intermittently powering off so I replaced the PSU with the one I got from iFixIt. What has me curious is that the old PSU wouldn’t buzz, but the new one does. Is this the same problem identified in the post above, did I potentially mess up the install, or might my new PSU be faulty?
I’d send that PSU back to the seller.
