Really appreciate the thoughtful, detailed response, thank you! I've not had many issues with my various Duet products, but when I do this forum has always been incredibly helpful.
I will check the cable crimps for sure, great idea (I created the cable from the Duet wiring kit). The cable is not shielded, and it is zip-tied into the wire bundle, so your point about noise from the extruder motor cable is very plausible; I will separate it from the bundle on the next run and see if that eliminates the false alarms. Perhaps I should even try a shielded, pre-made cable to eliminate both possibilities.
Sounds like my setup is similar to yours...I created a custom mount to place the MFM just before the BMG extruder....eyeballing it it's probably ~50mm or less.
I do have a long bowden tube to get outside of a normally enclosed case, but it is almost entirely pre-extruder. Collet clips are in-place, and I did carefully cut (and re-cut, sigh) the short tubes between the MFM and extruder, and extruder to hot-end, so there is no obvious flex when the extruder is pushing. Here is my setup:
HotEnd.jpg
Thanks again for all the great tips, I will check all of these as well as increase the measurement distance a little further, and see if I can eliminate the false alarms.