I have installed windows 7 on an nvida motherboard with creative x-fi card. It has crackling noise but I fixed this once before by altering within windows 7 the amount of installed ram from 4g to under 4g. I have forgotten where to do this in Win 7.
You can't change the amount of RAM Windows sees unless you uninstall it from your system. If the sound is coming from the card, I doubt that RAM would be an issue, you either have to update the drivers, change your speaker connections, or check to make sure your motherboard and audio card don't have sheilding issues (web search may help you with that last one).