I've tried several different versions of oscilloscopes from around here including the google code one, simple and tiny one but I'm getting the same trace "noise" on all channels.
I am using a Pro Mini with FTDI cable and seem to get noise. It seems to be related to the USB but is not transmission or receiving or Raw voltage or Vcc. I can only assume it to be a combination or interference from the pro mini circuit as the only thing i have added is the lead for probing.
maybe you could show what you mean by "noise".. I would have thought that anything in the USB circuit would be too high frequency to show up in the signal. what does your proble look line? have you tried grounding or shielding it?