Knocking sound when idle

nissan
sentra

#1

When I am at a stop light waiting for the light to turn I hear a knocking sound coming from the engine area. If I move the car into neutral it disappears, and it mostly occurs when the car is idle, but sometimes it occurs while I’m driving. What in the world could this be?!


#2

Could be just something loose and rattling.
Get a helper to put the car in gear and hold it in place then listen from outside (hood open) where the sound is coming from.