The files have to be exactly in sync and the same level. Line up the files exactly on two tracks of a montage, and invert the phase of one of the files (right click - invert phase). Then play them together. You might be able to adjust what’s needed (level or sync of the files) to accomplish what you want. It accomplishes the same thing that S-EH suggested (delta file), but allows pre-adjust if needed. If it does what you want, you can render what you’re hearing.