I am not sure if it's piston slap or what.When I start my car it makes a knock/tapping sound that goes away when the car fully warms up. The sound comes from the bottom of the engine. My 94 formula made a similar sound when it spun a bearing but that noise never went away and got worse over time. Is this piston slap? It also sounds kind of like a bad lifter. The sound comes back after the car has been sitting for 30 mins after being drivin for awhile.