Doug,

Well, it was worth a try, but the DPST switch did not fix the
problem either. It worked fine for about two weeks, then tripped
again a couple of days ago.

If it's *still* causing the GFCI to trip, then I see only two
possibilities:

1) the original GFCI *and* the replacement are defective

Seems unlikely. I've never had a GFCI fail before, so I can't imagine two
being bad, especially since they are two different brands.

2) there is a ground fault in the fan itself.

That seems to be the only thing remaining, though I don't understand how it
could trip the GFCI if the DPST switch cuts it out of the circuit
completely?

I wired the two bathrooms in our house the exact same way and we've never
had a problem with the fans tripping the GFCI's.

Anthony