1991 honda accord

4 cyl i believe it's 2.2 auto matic? it grinds when it's starts and i pushed it back and forth and had him start it back up never grind until you put it in reverce and it grinded then. is there a sensor gone bad? if you know you have to send me send me e-mail me if you know whats wrong? i think a sensor what do you think anyone?

thank's

scrapper.