Having experienced only machines my family and I have owned:
the PowerMac G5 is the loudest by far - when the fans go on
the PowerBook G4 is pretty quiet - we have two of them and they vary a bit
the iMac G5 is pretty quiet but if the fans go on full it can get loud
from what I understand, however, the Mac Mini is pretty quiet but I've only spent ten minutes on it at the Apple Store.
I actually used an iBook at the Apple Store and I thought it was rather loud.
Hi, I have an iBook and it's quiet, my eMac is some what loud but nothing that is mind disrupting, now a friend just got a mini and said it's really quiet comparied to my eMac and about the same as my iBook .
Well, i just got my Mac Mini, and it is practically silent. Honestly. Even when transfering 15 GB of files like I did last night, I didn't hear the hard drive at all, to the point that I thought it might have gone to sleep. The only time it makes noise is when it's reading a CD or DVD at first.
My dad has a G5 PowerMac, though, and it's a little bit louder, but not by much. It's one of the first 1.6Ghz SP's, and it runs really quiet too. Much quieter than our old G4's and G3's, and definitely quieter than my G4 PowerBook which blasts its fan every five minutes.
Mac mini's are the quietest desktop they are silent and stay very cool. The notebooks are all pretty much silent. The eMac, and powermacs are quite noisy but thats in comparison to silent computers they are far quieter than most dell rigs i have seen and the iMac G5's are quiet but not silent.
Powermac G5's sound like small lawnmowers
like..we have a computer lab at school with about 25 of them and if all the ones in your area bring the fans up to speed at the same time its extremely bothersome.
My powerbook G4 (which just arrived yesterday..and i'm quite quite happy with it) so far has only made sound when i'm burning a DVD or accessing something on a disc..and its only for a few seconds, not a consistent sound.
haven't had much experience with imac or mac mini..sadly.