crackling sound when using USB Headset

I am using a USB headset from Plantronics and keep having a lot of static and crackling noise whenever I am recording with Garageband (or any other app). The funny thing is that the sound was crystal clear when I used it for the first time and also after a clean-install of the system!?

So it seems that there is some kind of software problem which somehow creeps into the system after using the headset for a while.

Does anyone here know, how this could be reversed ?