I have had this "buzzing" sound inside my G5 for a long long time. Nothing nasty sounding, but if you listen to it you can tell its something attached to a fan because it speeds up and slows down its pitch. So I got a can of air and some pipe cleaners and went to town on the G5, pulled all but the top HD fan (can anyone figure out how to pull the HD fan without disassembling the ENTIRE machine, cuz I couldnt), that I just gave a once over. So it looks clean, but it still has the buzzy sound. What makes it difficult to pin point is when you remove the air deflector the fans go on full blast and U cant hear the low buzzing. So I figured out if i just move the air deflector out a tiny bit, leaving its 3 tabs in place, I can finally tell that my graphics card is the culprit. I pulled it a while ago and cleaned the fan/heatsink of dust, so its clean. So my question is, can the fan become loose somehow over time? I can still be wrong about the sound coming from the Graphics Card Fan, but it seems like it. Though to pull it and clean it again seems kinda silly.