This past weekend I purchased two H80s from Fry's Electronics in San Jose. These were from batch #12019402. Both exhibited the resonating grinding noise.
Tapping on the tubes would make it go away briefly only for the noise to eventually return. Laying the tower on its side absolutely made the noise go away--but who is going to lay their case on its side in a production environment. I stopped by Radio Shack to pick up a 1N4001 diode and slapped together an ugly but functional adapter. SILENCE IS GOLDEN. Also running it off the fan controller on the Corsair 600T drops the voltage enough to silence the pump. Nice design flaw and good job on the oversight Corsair.
Note: My PSU is outputting a measured 12.2V off the 12V+ lead.
I promptly packaged it all back up and exchanged both for two new ones from the same batch lot. The new ones were worse, as no amount of tapping the tubes would silence the grinding noise. Back to Fry's for a third round. With very little confidence in this product model, I opted to return 1 of the 2 and exchanged the second one.
The third-time exchanged H80 is from batch #11459402. So far running IBT for 24 Hours at Maximum @ 4.5GHz with 16GB of RAM--this unit is not making the loud irritating grinding noise. I don't have faith that it will continue to run silently so I am in dialogue with wlw_wl for a pair of his adapters because his adapters are so much prettier than mine.