I have two audio tracks which are mostly identical. I want to isolate the differences between the two. I can use Audition, Audacity, or really anything else.
Whichever app you use, you'll want to line them up and then invert the phase on one of them. Depending on how identical, and how they were made, it might easy to line them up and get an accurate result, otherwise you'll have to spend some time trying to line it up as best you can by zooming in on the samples.
The idea being that if you have two things that are the same, but have opposite phases will cancel each other out. Imagine a 2 samples being at 1. They are the same. Invert phase on one, and you have 1 and -1. Add them together and you have 0, aka nothing.