It could also be like doc al said with the flex plate cracks. I have a camaro and I thought the front pump was going out of the trans and it made a funny little clatering, tapping, grinding, hard to friggin explain sound and it was the flywheel. Cracked at the crank bolt holes on every hole except one. I'M LUCKY IT DIDN'T GIVE ON THE ROAD! Good ol' Chev brought me home though.