You should carefully inspect the CPU and the socket to make sure no pins are shorted by a tiny trace of heat paste. If they are clean, then the audio chipset may be faulty. Did it work fine before or did the sound issue start after removing, cleaning and reinstalling the CPU?
I bought a "new" motherboard on eBay which had AS5 all over the socket. I thought "what the heck" and stuck my CPU in. The result was bent pins, AS5 all over the pins, and a lot of cleaning. I soaked my CPU in alcohol like 10 times, and cleaned very thoroughly with an air compressor and paper towels. During installation, I made sure it looked perfect.
I really don't want to pull it out (finally got the thermal paste/ cpu cooler in correctly) but that may be my only choice.
So the CPU can cause this problem? Why would a CPU cause audio to mess up?
Thank you very much!