Hold on a second here. Your not giving us much information, we can throw guesses all day, but that wont fix the problem.
First, is the sound a sharp metallic click, or a deep clunk, a ping, is it loud, or soft. Where on the engine is the sound coming from. Saying the engine don't help us one bit. Is it high up, or down low, is it from the passenger side, or the drivers side, is it on the front or back of the engine?
How you answer this will give us a better idea of what is wrong. If you can make a video of this and post it, that will also help.
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