ok, shame on me, I've Just discoverd that the wireless (infrared?) Mouse placed near a PU produce some interferences, hisses, Noise in general.
I've partialy solved changing the model of mouse (still wireless but without upper light) and it's definedtly better,
but I wonder if a trackball type would have the same issue or not... or maybe will be even worst
any experienced mouse-jedi here?