AFCI Trips

[augie47]

Homeowner called electrician due to tripped breaker on the circuit to a blower on a gas fireplace. While troubleshooting, the electrician found the blower breaker tripped when the gas dryer was started (fireplace blower not running). He changed to a new breaker, same result. IN despiration, he changed the breaker to a different phase and it doesn not trip.
Any clue ??

 

[Electromatic]

I've heard (probably here) that some gas ignitors create some kind of a spike or harmonic disturbance that can trip AFCIs. I wonder if the fireplace and the dryer were on the same phase before.