Ways to determine approximate magnitude of crosstalk between PCB layers
As @derstrom8 suggested, there are better tools for doing this, but tend to be expensive &amp; aimed at pros.  I vaguely remember there is a FOSS field-solver tool out there somewhere, but can't remember.  But if I interpret your PCB stack-up figures correctly, you may be able to approximate your situation with the Saturn tool I mentioned:



If you set it to 'stripline' mode where you're calculating crosstalk of 2 tracks sandwiched within 2 planes, and then set the distance of the bottom plane effectively to infinity (500mm) because that doesn't exist in this scenario, then set H1 to the gap between your 2 inner planes (where the lower plane is your power track on the inner-bottom, right?), and H2 to the gap between bottom-layer &amp; bottom-plane (what you describe sounds like a typical 4-layer stack-up), I see -84dB, or 1.25mV.

Perhaps with that rough idea you can use your input-impedance &amp; knowledge of the broader system to work out how significant this may or may not be.