In the discussion about silencing a Power Mac 9600, I described what I did to silence a Power Mac G4 MDD: I replaced three fans and disconnected one (the side panel fan cooling the DVD burner, which I never use) — consequently the machine got remarkably quiet.
For your convenience I quote here below the rest of the description:
I placed one 120mm SilenX iXtrema 120 (noise level 18 dB, air flow 90 CFM) for the CPU, and two Xilence Slim 60mm Case Fans inside the PSU (22dB, 29.7 CFM).
I followed some instructions found here:
I faced just one problem: the iXtrema 120 sports three grey wires while there are only two pins on the motherboard, so I had to figure out which wires to connect (see photo — turned out the central wire is +).
The two 60mm fans are considerably slimmer and move less air than the original fans, but this doesn't seem an issue. Here's an image showing the new and the old fan side to side, and here's another one showing the new fans placed in the PSU.
Now I'm afraid the SilenX iXtrema 120 (whose task is keeping down the CPU's temperature) is not moving enough air, because when I put a hand near the fan I barely feel a gentle breeze. I tried comparing the iXtrema 120 with the original fan and indeed with the latter I felt way more air movement (and heard WAY more noise) — about double the iXtrema 120's. As an experiment, I tried powering the iXtrema not through the motherboard's pins but through an unused SCSI molex, and predictably the fan span at full speed, moving a lot of air (undoubtedly more than the original fan powered by the motherboard) and generating a considerable amount of noise (although less than the original fan).
My doubt is: could this «lazy» fan cause some hardware failure due to insufficient cooling?