It could be an exhaust leak, or something rattling like mentioned above. Are you sure it is pinging? All cars can potentially ping if you are luging it under a load, but not by just taking off. Does it make the same noise in the upper rpms? I am inclined to believe that if it is pinging that easily than it should also ping in the high rpms as well. If it is truly pinging and not something else then maybe you need to back off some of the timing with SCT2. What do you have your timing set at? If you have been running the SCT2 tune for awhile with no problems and this is a new development you could have potentially just have gotten some bad gas. Is you CEL coming on? Another thing that could be, is that if you drive the car pretty conservative potentially you could have carbon build up on the top of the pistons that is increasing your compression thus causing the pinging. You could seafoam it just to eliminate this possibility, I mean its a long shot but its a cheap thing to try.