paperclip test* is mostly useless, it can only determine that the power supply can power itself with no load. it cannot test that the PSU can support an electrical load.
if the whine happens on two differing motherboards it cannot be the motherboards. elimination leaves the PSU.
*paperclip test is like a mirror under the nose of a sleeping person. breathing or no that is all you learn. not how healthy, spy or vigorous. the PSU is breathing, but the spinning fans told you that.
how old is the ARC? if nearing 3 years I suggest replacement .
if under 3 years you can send it back for repair but you will have to pay for the labor costs for repair, parts are covered.