Apple cooling fan goes bonkers?

[pib]

I have a late model Dual G5 running Pather 10.3.8 and on some websites and WMV videos it seems like the fan goes bonkers. It used to stay calm and quite but now speeds up on some websites more than others. Should I be concerned? It's kind of annoying because of the noise. Furthermore, I have noticed a distinct correlation to going to ebay and my computer not starting up properly the next day. And searches on EBay take forever.

Any ideas? thanks!