For awhile now my car has been making a very strange rattling noise. It only makes the noise when I am stopped but still in gear. It doen't make the noise when I am in park. When I accelerate the noise stops. I Have no clue what this could be. When I am on the highway and I take my foot off the gas I can hear some grinding coming from underneath and I was sitting at a red light when the rattling (it almost sounds like a lawnmower) was at it's loudest the car just shut off and would not start back up. My mechanic said that its the starter. It's not making any sense to me. Why would the starter have anything to do with it? Any other opinions why my car crapped out on me today? I would really appreciate it.