i've got a 2014 T4R SR5 with 2200 mi on it. The last few days I have noticed that in the morning, for the first few miles of my trip, there is a faint knock when i'm stopped and my foot is on the brake with the car in D. It seems to go away if I switch it to N. Appears to be coming from the engine. After the first couple miles I could not hear it anymore. Anyone have any idea what this could be?