1) Disable and unplug sound devices you are not using
2) Reduce the mic volume to 15 (or keep it a bit higher if people can't hear you)
3) If you record reduce your output volume to 1 while you are recording (if doing commentaries if not CHANGE your headset to your front audio port and use your rear for recording).
4) If you can move your graphics card to the furthest slot to the bottom of the case.
5) Lift your computer off the floor if it is on carpet.
6) Ground your PSU
7) Ground your mini jacks before plugging them into the computer.
8) UPDATE AUDIO DRIVERS IF YOU HAVEN'T