The last time I tried to use my dual 1 GHz Power Mac G4 'Mirror Drive Door', I was blown away at how much louder it was than my 'Digital Audio' Power Mac with its dual 1.6 GHz upgrade. The MDD Power Mac is known to be noisy, and Acclerate Your Mac has a very helpful article on replacing the two fans in the power supply and the CPU cooling fan.
I ordered the suggested fans from NewEgg.com for about $18, and I finished installing them this morning. It took some doing, as Apple uses different power connectors, so I had to splice the old connectors to the new fans. That meant scrounging up my ancient soldering iron and some solder, buying a roll of electrical tape, and only burning my fingers once - very slightly.
I ran into a problem the first time I booted the system with the new fans installed - the CPU temperature quickly rose beyond 70 degrees Celcius. I found that the power supply was very hot, and the culprit was the new fans. They weren't spinning at all. It turns out they were catching on something, so I made a gasket with some double-sided foam tape, which solved the problem.
I am happy to report that the MDD is pretty much as quiet as the 'Mystic' dual 500 MHz Power Mac (scheduled to become our test server now that the MDD is up and running again) and the Digital Audio. This mod if not for the faint hearted, and it's letting me use my newest Power Mac once again. (Yes, it really was that noisy.)
Many thanks to Accelerate Your Mac and its readers for the article on quieting the MDD - and so many other wonderful reports on the site.