I have crackling/popping noises when listening to anything through my USB headsets. Through the green audio plugin there is constant ringing, I don't use that but it may be related.
BIOS and firmwares have all been updated completely on my Gigabyte GA-P55A-UD3 (rev. 2.0). I've stumbled upon many threads full of people with the exact same problem with their Gigabyte motherboards with Realtek drivers and Windows 7 x64.
Some people find that it is problems with their latency but I have zero problems come up in DPC Latency Checker. I don't have any throttling programs affecting my processor.
I have tried switching usb ports but that does nothing.
I have seen this often where the problem is a bad ground, even for a digital line like USB.
The question is how to test - The easiest thing would be to eliminate your OS. Download a bootable linux CD, they should all have the realtek drivers. If the problem persists, it is most likely hardware.
Reply to MDSIU, he said headsets, so... I could be wrong. if its just one, thats the thing to try first.