I seriously recommend all iMac G5 owners out there to check that the top of their imac is properly 'in' and does not have any gaps along the top or top sides. Maybe i am a complete idiot but i thought all this time that my imac had its back on properly and i have opened it and closed it a lot because i have been having real problems with my Extreme card. Anyways - the back wasn't on properly and hasn't been for 2 weeks or so. When i put it back on today after installing a new Extreme card (Apple support is great) i realised surely the top is not meant to have all the gaps showing and that the edges on the top corners were not aligned - before i assumed it was some sort of extra venting. And true enough i went to the manual to double check the way they showed how to put the back on. They mentioned angling it in as i did before but then realised the top gaps were meant to slot into the top gaps after about 20 mins i finally managed to slot it in. I hope to god i haven't cause any damage to the lower half as obviously more strain would be on that part. It seems now the imac is performing better..the buzzing has gone (?) and obviously the Extreme works perfectly now and the fans are quieter. So anyone else stupid enough to have their back of their imac on properly? I would encourage everyone to check I bet i am the only one..