[jluetjen]

What sort of fuel are you running? If you're running a "regular" grade, try adding a full tank of the highest octane that you can find. If the rattling sound goes away, it was pinging and you need to tune-up the car and confirm that the ignition timing isn't advanced too far. Your car was designed to run on regular unleaded and if it's still pinging on Super you've got a serious problem. Running a bottle of techron through the fuel system will also help clean out the injectors some so if the pinging is due to a lean condition from clogged injectors, it might help.

If the problem doesn't go away with the high-octane fuel, I'd suspect one or both of the chain tensioners.