gfci outlet

[ptonsparky]

Certainly a possibility.

Inductive kickback (don't have to originate on the same circuit) is another possibility.

...

Changing brands works on occasion but once in a while you have to look at every little thing.

 

[kwired]

Electric fence charger in the barn? Sometimes they don't play well with GFCI's, even if not protected by the GFCI.