Get a reference number for your calls.
Phone them EVERY time it happens.
Insist at a 450 mile round trip is out of the question.
They will either (a) have you ship it in for repair or (b) send someone out to look at it.
I would take a look at a small program called iStat. This will show you the internal temperatures of your G5 and may give an indication as to why the fans are running full bore.
I have an iMac G5 (w/iSight), running 10.4.11.
I've had two episodes where the fan inside of the iMac is blowing fast and loud. Once, it started when the iMac was in the sleep mode and I was "waking it up." The other time, it was already blowing hard when I entered the room. (I didn't do anything. It was just like that on that time.)
The first time, I couldn't seem to get the iMac to do anything. I finally unplugged the computer, waiting a minute or so, and plugged it back in. Everything seemed to be normal. I still called Apple (I have iCare) and reported it.
The second time, I called Apple again, just while it was still blowing hard. The specialist had me power down, power up, and then run the utilities to check the hardware. Results came back nominal.
Both times, I reset the PRAM too.
Apple told me after the last time that if it happens again that I should take the iMac to the store for checkout. I'd rather not, as the closest store is 225 miles away.
I've also had some noisiness from the CD/DVD drive. It's run loud enough that people on the Apple end of the phone (on other trouble calls) noticed. Otherwise, the functionality of the unit is fine.
I'd appreciate any feedback about this issue. Thanks.