I was morning and had to stop and shut off the mower to answer a call. When I went to restart the mover a couple of minutes later it turned over very hard and the starter solenoid rattled like the battery was dead. Tried to jump it with a car with the same result. Though the starter may be failing so I replaced it, same result. I tried a different battery and watched the fly wheel. The engine is turning slowly while the solenoid is rattling, and it will turn easily for a 3/4 rotation the pounds through it again. Any ideas on what is happening?