Thanks for the link. I've already contacted HP Support. They first suggested replacing the power adapter, but after some searching I found a post by another user on cnet forums that had exactly the same issue (he even checked other models in store to confirm his claims), so it's a fairly strong bet that this falls within their QOS. I did tell support to forward my complaint to the design teams or wtv though.
Good news is the noise isn't overly disturbing - but it's there, and this _is_ SPCR. However since it's a network printer it's cheap and easy to move it away from you. I find it particularly annoying that the sound doesn't go away when you turn if off.... why does a printer need to use power, however little it may be, when it's off? An article for EPCR