I have a MTD Garden tractor/mower. I heard a whinning sound while cutting grass. I shut it down but the sound continued. Discovered the starter was spinning. Could not stop it by turning the key. Disconnected the Negative side of battery and it continued to spin. Then, each time I touched the negative wire to the battery, it would try to start the engine again. Finally, I disconnected the Positive side and it stopped. Is this a solenoid problem, or a starter problem? Also, when I touched the negative wire to the battery (With the positive still attached) it was like the terminal was magnetized. Is there any help out there in cyber-space?

Its either the solenoid sticking, or key switch... I'd bet more on the solenoid.