I've just got my iBook g4 back from having the standard issue 40gb HD replaced with an 80bg 5400rpm Hitachi drive, I've also just installed another 1gb RAM, taking me to 1.5gb . The computer's working fine, a fair bit quicker too, but I've noticed that since I got it back the fan (at least I think it's the fan not the HD) is running constantly. It's not particularly loud but it is noticeable in a quiet room - and it's particularly noticeable to me because the iBook was completely silent for most of the time before, except when it got hot. Maybe I'm being pedantic, but is this something I should be concerned about? EDIT - OK, as the sound seems to be coming from under the left wrist rest I'm thinking it's the hard disk. Maybe it's just louder than the old drive? Seems strange that it's a constant noise though.