Within the last few months I have had issues with our master toilet. When I run water elsewhere in the house, (pretty much anywhere: sink, toilet, shower, etc), when I turn the water back off the toilet upstairs runs for about 3 seconds.

I can't pinpoint exactly when the problem started, but around the same time it started I flushed out the hot water heater and I adjusted a venting leak around the drain pipe in the basement. Other than that, I am at a loss with this one.