Chevrolet Repair: engine pinging noise, or valve train noise, gmc sonoma, exhaust leaks

Question
I have a 03 GMC sonoma with a 4.3 V6, and auto. It has 14500 miles on the engine. When under load at light throttle the engine sounds like it is either pinging because of timing or it has valve train noise. I took it to the dealer and they swear they can't hear anything. Is there any timing adjustment that I can check , or is it controlled by the computer? Do you have any other ideas? I checked for exhaust leaks, and found none. I added higher octane fuel and it didnot change. I have only had this truck for 10 days. I feel like I have been ripped off.

Answer
Everything is controlled by computer, however, You can return it to the dealer, under warranty?, Take the service rep. for a trip around town or whatever, to have both of you witness this noise. When heard, and you both agree that there is a noise, probably "pinging", you tell them that you want this eliminated/repaired. IF, they balk or give some excuse that its "normal" or something your not comfortable with, just tell them you want to speak to the GM area rep.(nicely)!! You should see/hear a new tune!! The last thing they want is a customer wanting to complain to the GM area Rep!! From here, I'd guess it's the knock sensor not reading correctly. Also, I assume this vehicle is still under warranty!?  Good Luck!