frankap

hi I have a Variax 500 and it worked well with XPS-AB until now: XLR thru PA - 1/4" trhu a Marshall Amp. Recently, if I switch XLR to PA, it works well and the 1/4" signal is mute; but when I switch to 1/4" the sound thru the amp is good, but at the same time in the XLR signal (that goes thru the PA) there is a noise and not mute. Help! Frank