First thought: Invert the phase of one of the tracks 180 degress, then sum them together. Anywhere the is a bump in the waveform would show a difference between the two sources.
Funny, you can use this technique sometimes to pull clean vocals (for remixing) from certain kinds of music (they have to be panned center in an otherwise stereo mix):
a) reverse one of the channels and them sum them and you'll sum will contain only stereo data
b) reverse and sum (a) with the original track to get only the mono content
