Seen it before with budget motherboards - not much you can do except get an external / USB sound card. I am using a Sound Blaster Play!3 because of that exact issue, most noticeable with the mic input.
You can try and see if improving the grounding helps - making sure your outlet has proper earth ground, checking the mobo screws are snug enough and not using any washers (needs proper metal contact to the case), making sure the I/O shield is installed and tight and has the flaps that ground the rear panel to the shield. You can also try getting a bootable linux like ubuntu
and see if it is a windows driver issue, may be a good first step since you just need to boot from the USB stick.