Check in the bios for the three voltages your psu outputs...3 volts, 5 volts and 12 volts. They should all be within 5% of the three figures I gave you. If not, switch out the psu and see if the crackling issue goes away. Beg, or borrow one. I hate to have you buy a new one and it not be the issue.
Voltages are within 1%. Thank you so much though, I hadn't thought to check that. Also, as of today I have now Reformatted, removed the X-Fi card, checked all cables, backed off my overclock and pulled the mismatched 4GB DDR3 kit out of my system leaving an 8GB DDR3 kit. It's such a subtle thing occuring at intense points of audio during music and games. I've tried switching between all of the different bitrates and frequencies, makes no difference. I'm really at a loss here and I hope I don;t have to RMA this motherboard, it's less than a month old! I've adjusted every BIOS setting I can think of... Nothing works, just get this same crackle regardless of whether I use speakers, headphones or my Hi-Fi system routed through my DJ mixer... So frustrating. Thanks to everyone who's peeked at this so far though.
Edit: The onboard audio on this mobo is the Realtek ALC887 HD chip