unhealthy "rattle"

Shamrock

Hey,

I had posted previously about a rattle/knock and after tinkering around I think I can describe it better. My car is a 7AT with stillen headers\test pipes and an akropovitch full system exhaust. It was tuned and one of the throttle maps from the forum was added. Basically the rattling occurs at the 2500 to 3000 rpm range and it sounds like it is coming from the engine area. It doesn't always happen but I can always reenact it as follows; semi-hard acceleration in a high gear (five or six) from low rpm (2000 rpm.) Is this knocking, pinging, timing or perhpas nothing? I had been driving for two years without a tune and only with the above parts and I believe this started happening after the tune. My car only has 33000 km and I'd be petrified to think that I have done something that is causing damage to my engine. What say you all? Thanks