thats weird because i never had a noise problem w/ the northbridge cooler on my dfi ultra.
Anyway one day i was bored and did some stuff on the board, i also popped the fan off, removed the thermal tape (its crap)...and put some nice AS on the northbridge and put back the fan... (i also isolated the parts around the northbridge with electrical tape to avoid a shortcut)...anyway i think i remember i got better temps after i mput it together again.
What are your temps ? My NB temps (idle) right now is 43F