I can hear a knocking sound while idling.
The description you have given is rather vague, but it could be that what you are hearing is timing chain noise. This engine is well known for having timing chain issues. In fact, Chrysler even issued a recall for this problem. Timing chain noise is usually worse upon start up and can be described as anything from a rattle to a knock, depending on whether the chain is hitting the timing cover or not. Of course, without hearing the engine this is just a guess. A trained mechanic, such as one from YourMechanic, will be able to diagnose and repair your engine noise.