I bought the vehicle, and about a week later noticed a slight ignition knock. I discovered that this was due to a failed intake manifold gasket on the bottom of the manifold. to check this, remove the pvc and breather from the valve covers, and put your hands over them; if there's a good strong vacuum, this is your problem. chrysler has a technical service bulletin out, yet the dealer did not check for this, despite having done a "presale inspection". i smell... BS!