2 or 3 times a day, my toilet sounds like it is filling up - you hear what sounds like water running into the bowl and then a shut off noise but it is not flushing. I've taken the lid off and checked. I don't see any change in my water bill so I don't think there is a leak. Sometimes there is a gurgling sound for several minutes but also stops.
I've lived in the house 5 years but it is the original toilet from 9/1999. It looks to me like the insides are not the original.
Any ideas what this might be and how to stop the problem? It's actually woken me up in the middle of the night.