Engine Coil Pack Bad?

It could be lifters tapping, spark knock, or any number of things. From what you are saying my guess would be spark knock. Have you checked the timing? When you replaced the plugs did you replace the cap and rotor as well? I haven't checked the timing on my wife's '01, but it does the same thing. It is spark knock on my wife's car. It looks to have a new coil pack on it. So after spark plugs, cap, and rotor I plan to set the timing and go from there. Let me know if you figure anything out and I will do the same.