Never or when it dies. I replaced a Corsair 450 gold due to buzzing. Turns out it was the Corsair case making the noises.
loose screw or rivet + hdd/fan vibration = case noise.How does a case make noises?
I am dreading possible ATX12VO adoption outside of the OEM markets. Would instantly obsolete a few PSUs I have lying around including the big one I just bought.