The sound generated by Power Mac G4 (Mirrored Drive Doors) computers is approximately equivalent to previous dual processor computers. Users who upgrade from earlier, single processor computers might notice that the computer is louder. This is because there are more parts to cool--multiple processors and additional expansion capabilities--within the same form factor.
However, Apple has found that there are some situations that may lead to increased sound levels beyond what is expected.
One is addressed with the 4.4.8 version of the firmware (BootROM) for your computer. See software download document 120171 "
Power Mac G4 Firmware Update: Information and Download" if you have an earlier version. You can tell which version of firmware your computer has by using Apple System Profiler.
Other situations include the processor fan constantly spinning at high speed, and a clicking sound that comes from the computer's power supply. In both of these cases, contact an Apple Authorized Service Provider (AASP) to determine if your computer is affected by either of these symptoms. Apple has directed AASPs on how to address affected computers.