Stop the noise of the PowerMac.
If you have a PowerMac G3 (blue and white) or G4 tower and you find them quite noisy, we can tell you that the magana is very likely to be found in the area of ??the big fan, but don't worry, the fan works well, the problem is perhaps the vibration of the same.
We remind you that any tampering will void the Apple warranty.
It is very simple: proceed by removing, unscrewing, the metal arm that holds the fan hooked to the plastic case of the PowerMac and stick a thin layer of artificial sponge in the holes of the screws so that they cushion the contact between screw and iron plate.
Merit honor, the solution was found by xlr8yourmac and we refer you to the site to see the illustrations that clearly explain the intervention.