GFCI & radio static

I put a new GFI outlet in my basement for a sump pump. There was already an outlet there, I just replaced it with a GFCI.
When I flipped the power back on there was a flash, and the GFCI tripped. [I don't think the breaker did-- but I'm not sure.]
I took it apart & examined the GFCI. There was some carbon on one end but I couldn't see anything that looked like it had arced. Other than smoke residue I couldn't see anything wrong inside the box-- so I wrote it off as a bad GFI & replaced it.
A few weeks later the GFCI tripped while I wasn't there. I reset it & it was fine. . . until that night when it tripped again. It tripped one more time in the next 24 hours-- so I bought yet another GFI but it hasn't tripped again in several weeks.
Yesterday I unplugged the sump pump to do some work & noticed the cheap clock radio that I was listening to go significantly noisier. Plug in the sump, the radio clears up. It was repeatable several times. Whether or not the pump is running doesn't matter. If it is plugged in the radio quiets down. [the switch mechanism on the pump is one of those diaphragm types that has no visible moving parts]
I've plugged one of those cheap circuit checkers [that plug in with the 3 lights] & it didn't complain. I also had a Kill-O-Watt plugged in to the outlet for a week or two & it wasn't indicating any leakage.
Any ideas what I'm looking for? Why would an appliance that is [apparently] working properly and not running have any affect on a circuit?
Thanks, Jim
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Did you check using the ckt checker with the sump unplugged? It almost sounds like the sump is providing the neutral/earth for the ckt. There might be a problem with the wiring so check it with nothing else plugged into it. BTW, that's a very dangerous place to work if there are any exposed voltages anywhere. Even neutral CAN be hot under some circumstances.
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Jim Elbrecht wrote:

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A sump pump receptacle is not required to be GFI protected. It fact it would be better if it wasn't. You wouldn't want that GFI tripping while water was coming into your basement. You have already experienced nuisance tripping. Your problem is not bad GFI's, It is lack the of experience of the installer. Just install a single receptacle (Not duplex) and you will be compliant and can rest easy.
I suspect that the flash that you experienced was a result of one of the wires being shorted from you pushing the GFI into the box.
John Grabowski http://www.mrelectrician.tv

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