Problem 1: Water Trickling Into the Bowl, or "Phantom Flushes"
You may periodically hear your toilet begin to spontaneously refill, as though someone had flushed it. A toilet that cuts on and off by itself, or runs intermittently, has a problem that plumbers call a phantom flush. The cause is a very slow leak from the tank into the bowl. This problem is almost certainly caused by a bad flapper or flapper seat. The solution is to drain the tank and bowl, check and clean the flapper seat, and replace the flapper if it's worn or damaged.