cubase 6 noise problem

hey guys lately ive been having this pretty noticable scratching noise i hear only in my sequencer(cubase 6) whenever i load any kind of plugins. if theres no plugins in the project theres no noise, and also when i mixdown doesnt mixdown the noise. Im not sure if this is a problem with cubase, computer, soundcard… ne ideas?

SCope pro pci soundcard, windows 7 64bit, cubase 6 64bit

hey little update, just tested the soundcard on a different pc (32bit), and no noise
returned the card to original computer and noise still there, happens with any plugin.