2007 Honda Odyssey Irregular Knocking Sound at Idle

My wife has, on 3 or 4 occasions now, heard an irregular knocking sound coming from the engine. I have been unable to replicate it and was, therefore, doubtful that it was serious. Today she sent me a video (with audio) of the vehicle at idle and, sure enough, a very strange tapping/slapping/thumping sound can be heard. There are no engine lights on, no maintenance minder lit up. The vehicle has had its timing belt and spark plugs recently replaced but, per my wife, made this noise before that time. I'm kind of lost as far as what the next step is. It's very difficult to replicate, seems to only come at idle, I don't know if I should take it to the dealer yet or wait until I'm able to replicate the incident.