I am using RF magnetron sputtering for deposition of Nb with WO3 film. W target being deposited by DC sputtering and is working fine, while doping Nb and turning on RF power even at very low power i.e 10W, I am facing noise from the supply. I even tried stand alone RF system for W, WO3 and Nb targets, every time I have faced same issue. Returned the RF supply to manufacturer but according to him its working fine, no noise issues . . . what can be the causes ???