Will a sound card stop this?

Have you re-installed the drivers for your onboard sound? Give that a shot. At the same time make sure all ATi drivers are removed from your system. It could be an old driver causing issues.

i have literally tried everything, re installed all drivers, re installed windows, used a different hard drive, messed about in bios and nothing has worked, i cant even get sound through headphones  

check that your video card in all the way and the power connected to the video card is fine. check your 12v rail of your power supply if it a cheap or old power supply it could be making ac ripple and sending into the mb and your sound card/speakers are picking it up. or the 12v rail is to low to run the older video card. check your pc to see if there a sound card or another card next to the video card..you could have an irq or dma issue. check the bios to make sure the irq set to auto and the sound set to default. check your speakers that there in the right port...also try a set of head phones. also check that all your power and front panel cables are not near each other.