Ok here's something to ponder maybe??? About the problem OP has.

http://www.whale.to/b/simons.html Hope this helps. Under the "Big Con" they talk about pinging of engines, and in the beginning of it too.

 

take a stethoscope or screwdriver and put on front cover. I bought an 02 with bad tensioner bars when the plastic on the bars wear out the chain is running on the metal perhaps giving you a ting. just a thought it had no codes on scanner professional job to change those blew my truck up just saying

 

have you used any quality parts or all junk yard parts????