SDL sound delay
 

Hi all
I'm working on some opengl demo stuff (ubuntu opengl sdl), and have had a couple of concerns and am unsure if it's drivers or a RAM issue. I know it's not my sw as it runs on my Nvidia laptop OK and my friends Nvidia PC.
The PC I'm testing on is a ATI Fusion using catalysis drivers. The board has 2GB of RAM, I've split the RAM via the bios to have 1.5GB RAM and 512MB of video RAM, going more that 512 stops ubuntu working correctly.
Basically what happens is when I'm running my software the sound(SDL_Mixer) is always about 1/3 of a second behind on ATI (not nvidia), so I shoot and the soound happens a split second after the event.
Also the frame rate is good, however every so often for what seems no reason ( ie not high poly model or not lots of shaders ) the frame rate seems to drop right down, this lasts 3-10 seconds then goes up to full speed.

Could this be a result of only having 2GB of RAM? If I go up to 4 will it help? Has anyone else had these issues?

Thanks in advance!