I am using both channels to look at digital signals in 1MHz to 50MHz range. I see at least 20% crosstalk of one channel superimposed on the other channel. Both channels using provided scope probes, grounded at the board or not I see same thing. Is there a common-ground problem? I ask because I can leave the probe grounds floating and still see proper signals on scope, so gnd is through the USB/PC/AC line gnd?