re: AFCI - Breaker keeps tripping.

Fixed this issue last week for a client. GFCI outlet (one of three) in the garage would stay tripped. Nothing wrong with the outlet at all, turned out to be the fault of a lazy contractor and electrician who had installed a seperate circuit for a backyard water feature. The pump was originally plugged into an extension cord that was direct buried then plugged into an exterior outlet. They just cut the extension cord and left it buried and plugged in when they ran the new circuit, when enough rain had saturated the ground it started tripping. If you've had any recent work done then it's possible to have had a line damaged. I've also seen the same with exterior outlets in decks and patios where the seal had deteriorated with age and would just let water in until corrosion became the issue. Unfortunately without specific test equipment that's generally beyond what even a dedicated DIYer would invest in, it's hard to trace live wire faults inside of walls, attics, etc.