This is associated with the answer from ballengerb1 a short while back, on toilet water tank issue.

I have checked and the water level is rather high. It is right on the brink of the overflow tube opening. Just this morning, while sitting on it, I kept hearing whistle noise from the tank. Also, very often, after shutting the sink faucet next to the toilet, I hear drip noise and/or sipping noise.

This means that your ballcock shut off float is set too high. You need to adjust this float so that the toilet shuts off way below the run off outtake pipe. Just a slight bend in the rod holding the black float ball should do the trick.