Comment 0 for bug 34723

There is no support for the thermal fans in any of the iMac G5 computers in both Breezy and Dapper (Flight 5). The fans will run at full speed and are very loud.

Apparently there are fixes around for this but they have not been implemented into Ubuntu, and they are beyond the average user.

Internet fixes:
http://lists.debian.org/debian-powerpc/2005/10/msg00414.html
http://www.linux-m32r.org/lxr/http/source/drivers/macintosh/windfarm_pm81.c