hahah jim-bob beat me too it... I think my modding a USB header with wake on USB enabled is probably the easiest way....
+5VSB should be on pin 9 of the ATX connector...
If you have a look at your PSU specs, you may be in luck. It'd take a bit of work and you'd probably have to splice the ATX cable but you can tap into the +5vsb rail which provides power to the system even when it's not running for things like wake on lan and wake on usb.
If you can't manage that or don't want to mod anything then the only other ways i could see this happening are either using batteries, using USB via a spare mobo header, find the +5v pins and do a bit of creative wiring. It should work if you turn on wake on usb in the BIOS, but watch out for the current draw of the LED's.
As for the PSU whining, I've heard thats pretty normal these days
you could try tapping firmly on the side of the PSU a couple of times to see if it goes away, usually it's caused by an inductor or other component vibrating but I wouldn't get your hopes up, the rest of your rig is pretty immense too and you're probably running that Enermax close to capacity.
Good luck with this, if you do decide to do the LED mod please post pics!