Originally Posted by
staffsMike
It's possible that the top fan distrupts the air flow to a downward facing fan on an HSF (big typhoon) and possibly the tower style ones ..Try unplugging that fan and sticking a book over the hole and find out.
Pretty sure the fan gaurd is just clipped in so it should come out..the fan should come out easily enough then. Read the manual it may be in there.
I think I'd rather give the the PSU the fresh air and just buy one more fan for the HDD or just not bother..
EDIT: Just an after thought, in most circusmstances no cables need to route through the hole at the top of the PSU section, they can all be routed around the back of the mobo tray..this might help when installing it..