I am driving an Acura 3.5RL 1996 model. I had a problem with emissions so when I had it checked, the shop guys said to change the engine. I changed it and after 3 days I hear this weird yet fast clicking/knocking noise coming from under the hood. I popped open the hood and listened for the sound. It seems to be coming from inside or under the engine. What might be the problem? Can anyone help me with this please?