It sounds really loud, like something is perhaps vibrating. It recently started but I turned off the G4 and it went away. Until a couple of days ago, now it starts not too long after booting.
I opened the case and decided to wait for it to start, as it sounds like it may be coming from the fan or perhaps power supply (though I have never heard of a power supply making funny sounds). Oddly enough, if I blow on the area with the fan and power supply, the noise starts up.
So if it is the fan, where can I get a replacement?