(sheesa gotta gassa goinga outta the wronga place-a)
Well, if it is indeed an exhaust leak, you should almost be able to hear each individual "tick" (if you will). If it were pinging, I doubt that if would be confined to just one cylinder, and therefor sound more like chains rattling rather rapidly. Right?
The reason that you wouldn't be able to hear it at plain ole idle, is that there isn't much combustion to speak of, going on at that moment...once you step on the gas though, you instantly increase the volume of gasses wanting to take the shortest route to freedom.
So far the exhaust leak sounds like the most plausible explanation for da noise.
"...rationality of thought imposes a limit on a person's concept of his relation to the cosmos." -Nash
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