Is your mic jack a 3.5 mm jack? If so, you have a few choices. Try a different pair of headsets with mic and see if your mic jack is still producing static. If not, it's the headset, if it still presits, you've confirmed its the jack. Then either replace the case or mobo depending on where you plug in....extreme and not cost effective. The other alternative it to use one of those usb/3.5 mm adapters. I've seen them at my local WalMart for about $20....could be worth it.
Just came to me...look inside the case...could be a bad connection from front panel to mobo or something pushing on the front panel connection just enough to cause your issue. I've heard tale of it some where...just can't place it.