More issues...alternator problem?

Got a 2000 Navigator. It would occasionaly die but it's been happening with more frequency now, as in almost every time I drive it (which is not much, only about twice a week). It only happens when I'm moving very slow, as in getting into or out of a parking spot, or when I'm stopped, like at a red light. It will quit on me, but if I throw it into park and hit the ignition, it starts up with no problem. A friend thought it might be the alternator. I should also mention that for about as long as I've had it, 2 and a half years, I hear grinding all the time, usually after I've turned it off and parked it. Could I need a new alternator? I put in a new battery almost one year ago. Thanks!

Remove the alternator belt and spin the alternator you will hear a bad bearing.