I've been having an issue lately with my PSU. When I stand my case upright (Zalman Z3 Plus) and power the computer on, there's a noise akin to putting your fingers between the blades of a spinning ceiling fan. The strange part is that the problem disappears when lying my case on the side with the bottom of the PSU facing out. Temps and performance are all normal, just concerned about this is all. Perhaps a loose fan? Any help would be great, TIA.