Has anyone found a quiet fan that gives adequate cooling for the CPU ?
…and here we go again for the zillionth time
Short answer: No, not really. Small improvements, maybe but the laws of thermodynamics and physics in general say there can be NO magic solution to force large amounts of air through a confined space without making significant noise in the process.
Real answer: If you search the Forum for things like… oh, I don't know…fans?
Seriously: fans, MDD cooling, MDD fan noise etc. There are endless discussions to be found here up to and including elaborate case mods, fan speed controllers and on and on. This is a conundrum. Much like a muscle car, the MDD took the 7450 chip (already a hot box) and pushed it as far as possible. Then they crammed 3 IDE busses, PCI slots, fast (for the time) video cards AND the kitchen sink into the slick curvy plastic case to make the "ultimate" G4. So, just like cramming a giant motor into a muscle car and tuning it for maximum power, it makes noise.
There are lots of good (and bad, VERY bad) ideas to be found here for improving MDD cooling. Just remember: PHYSICS. You can push the boundaries, but you CANNOT exceed them.