How do I know if I have a rod knock or if it's a different type of knock? I just noticed that when my car is warm I can hear a knocking sound coming from the engine.. I can hear it inside of the vehicle.. It's not very loud but it's there... It doesn't knock when the engine is cold.. Only after it warms up it starts doing it.. When I rev the engine I do not hear it getting any louder.. Please help me out.. What can this be?