Well i changed the spark plugs and wires and also the coil pack but then i go to

What is your question?

I go to turn the motor on i hear this loud knocking noise which wasnt there before now im afraid it could be the timing chain or a rod bearing i had someone look at it and they said it was the cat. Converters that were bad and needed to be changed i dont agree with that theory the noise sounds to loud for that to be right. This problem happens now everytime i turn it on its so loud that i dont run the engine now.its a constant thing. Any answers to my problem hopefully i can fix it without replacing the engine