Definitely sounds like pre-detonation. Odd though, the engine managment system should not let that happen... ????

I would NOT do any hard acceleration until you get it looked at. I put holes in the tops of two pistons in my superchared Expedition due to pre-detonation. Normal driving that does not cause the sound to happen should be ok for now.

Have you been thorugh a few tanks of gas?? Maybe you got some bad, really low octane gas ... ????