Static distortion @ DAC XLR connection

Hello everybody ! I have a strange situation. I heard that balanced XLR connections are much better then unbalanced RCA which I used until now without ANY problems at all. So I bought 2 pairs Mogami cables with Neutrik connectors aprox 60$ / pair. I connected preamp Advance Acoustic PX1 to monoblock power amps Advance Acoustic BX2…nothing wrong there. With other pair I connected DAC SMSL SU-8 to preamp PX1 . When I use digital signal over COAX from Denon SD/USB recorder DN-700R there are no problems. When I switch on DAC to USB B port there comes distortion that sounds like discharging of capacitors ( pk pk ) . I use German Inakustik Exellenz cable USB A to USB B to connect laptop to DAC. Also every time when VLC player goes to next song there comes same distortion ( pk pk ) …but never within playing song. Later it disappears, but comes back after changing inputs on DAC. Distortion is always present when switching inputs on DAC also @ low volume levels ! …Should I buy a new DAC ? Has anybody recommendations within price range 500$ ?