i know what you mean bro .. sounds like a torque converter problem ,,
by grrrrr do you mean trying to move while you have your foot on the brake ???

its not supposed to go into neutral or anything it stays in gear it just goes back to first gear when you come to a stop .. like they said does it still grrr or what ever in just drive or only od or what gotta lay out the specifics if ya want a specific answer ya mean lol