If it's still under warranty, as was already mentioned, get it to a dealer as soon as practical.
If you're out of warranty, can you be more specific about the problem? Any DIC messages or lights? Was this a one-time-only sound (ie: *tink*... silence) or repetitious (ie: tink, tink, tink, tink)? Has it happened again since, or has the car otherwise driven normally after that? Any other noticeable changes?
You mentioned that both times it sounded like you were getting heavily into the throttle when it happened (once to rev the engine, and a second time to accelerate through a green light). Can you reproduce the problem (ie: can you make it happen again by hitting the throttle)?