In all honesty, there could be a myriad of possibilities causing the probelm. Most likely, your headset is receving some sort of RFI (radio frequency interference). Likely sources are your PC/notebook, your cell phone, a home wireless phone, a radio/TV nearby, etc.
It could even be a poorly grounded electrical system.
So, what can you do? Try to minimize anything locally that could causing the problem, like moving other wireless device/emitters farther way from your system.
What sort of system (desktop or notebook) is your headset connected to? What model of headset are you using?