Probably several hundred gigs before I ever started bringing earplugs! (slight exaggeration) And I run a machine for 12 hours a day.
I guess I mean in comparison to that duct fan I bought the PCs fan is relatively quiet, the duct fan is definitely around hair dryer level but it changes in pitch which is additionally irritating. The fan is actually mounted out by the window frame, blowing outside air through a length of flexible ducting, into the first T outlet on ground level shelf, then up to mid level shelf T and then at last out the top L duct outlet.
I see my radioshack fan is 25 cfm... imagine 10x more air!
I'm still not sure how to power something like that though. I'd like to mount the power cord and controller switch into an electrical project box (blue plastic box that components can be wired to).