Freezing when waking up & strange noise

Hi everyone

I'm having a few problems with my Imac G5, started about a week ago, my girlfriend did the mac software update, and i think it updated the sleep light or something. Then the mac worked ok all the time it was in use, but when i wake it up from a sleep the whole thing locks up, then the fans go mad.
Now the problems have got worse, it intermittently boots, sometimes i get a grey screen then the little folder with the flashing question mark, i'm also getting a loud static crackling noise when I turn it on that can last a few seconds or a few minutes till the fans come back on.
I've zapped the pram, and reset the firmware but it hasn't helped.

Anyone got any ideas??

Sorry about the long post!

Thanks

no ideas? diagnostic leds are fine on mobo and it passes all the diagnostics ok, power supply? hard drive? ram? am i the only person with this problem?