Hi Cris
Yes this is a known problem with dual 1.4’s. What i have done with mine is a little extreme, but works well. I have removed all the drives from the tower and put them in external hdd cases. this removes the restrictions to the airflow inside, and cuts out the heat generated by the drives themselfs
This should be enough to sort it out.
Also make sure that the preforated intake grill ( inside, behind the four finger holes on the front) is absolutely free of dust and lint.
I also fitted two small fans here from a pc overclocked cooling system and took out the now empty hdd cage – you can leave in the back cage with one drive in it as this assists the air to go via the heatsink fins arround the processor.
The big fan inside normally runs resonably quiet but there is a thermal system which triggers the fan on flat out if the processor gets too hot – the trick is to make sure that the air can get in and out, so keep the airways free and the tower away from the floor.
Do Not open the side door as this will stuff it up – not fix it.
TMHO this was the reason Apple redesigned the G5’s with such a good cooling system for the subsequent models….
cheers
bruce