Had a funny one happen yesterday. The kitchen garbage disposal was running, but sounded like it was full of scrap iron because one of the rivets holding a flail onto the spinning macerating disk had loosened and letting that flail chatter against the housing, making a horrid scraping.sound.
I picked up a same brand/same size replacement disposal at HD and got it swapped out in a record breaking (for me) 36 minutes, winning my bet with SWMBO who scoffed when I told her she's be able to use the kitchen sink in 45 minutes or so. (She's usually the winner, my repair project time estimates are generally low by at least 200%.)
When I turned on the water and flipped the wall switch, the disposal motor didn't start. After saying, "WTF?" I tried the electric can opener which I knew was on the same circuit as the disposal. When it didn't run either I went down to the panel and found the GFI breaker for that circuit was tripped. I reset it and when I came back to the kitchen the can opener worked fine. I flipped the switch for the disposal and the GFI breaker popped again.
I checked my wiring at the disposal and to my embarrassment I found that the stranded neutral motor lead wire hadn't "caught" in the wire nut, and was just hidden inside it, but not connected to the supply neutral. Things were sort of tight and cramped inside the wiring compartment of the disposal, but that's really no excuse for my sloppy job, is it?
Anyway connecting that motor wire to the neutral side of the supply put things right.
I'm assuming that the motor's winding to ground capacitance caused current to flow through the supply side of the GFI which wasn't returning on the neutral side, and that unbalance tripped the GFI.
If it wasn't such a PIA to crawl under the sink again, I'd disconnect that neutral lead and test my theory.