I am unable to run either QT movies or games requiring OpenGL on my PPC6500/300 without getting distorted sound, static or jerky motion. If I revert to an older version of ATI software and older version of OpenGL, I do not get the sound distortion but, of course, cannot run some games that require the latest version of OpenGL. I have found comments on other forums regarding the PPC 6400s & 6500s having similar problems. I do have a Sonnet Crescendo 400 L2 G3 card installed. I have disabled that but there is no difference in results.
'Ello,
I’ve had similar problems for the last six months on my ATI Rage based card. Posted on many forums but no solutions. Then I found the holy grail of sites for STI Rage users:
http://www.rage3d.com
These are not official drivers, but as you will learn from reading a few posts in the forum there - they are much better. I downloaded version 7.5 of the drivers they have there and it solved my opengl problems - I suggest you do the same.
If you have any problems with them, post on the forum there and Slaykill or RageLTMan will be sure to help you out - they helped me 
…wow I sound like an advert - good luck
Ash aka EnglishMafiaGuy
englishmafiaguy@blackvault.com