I am hoping someone might know what this could potentially be. I typically start my car, let it warm up, and then head to work. About 2-3 minutes into my commute I usually get stuck at a stop light. This is when I hear what sounds like someone knocking on a wooden door. It only happens right after start-up when I am stopped at the light. On the days when I make the light I do not hear it. It is 4 consecutive knocks, like I said, like a knock on a door. The sound seems like it is coming from the passenger side rear of the car. The first time I heard it my wife and I were coming home from dinner and we both turned because it sounded like someone knocked on the car to say hello. I haven't a clue.
I have no warning lights, no squeaks, no rattles, etc. I am at a loss. It does not happen everytime so there is no consistency so I do not feel like it could be replicated by a tech at the dealer.