My honda city engine has recently started producing a tuk tuk sound at regular intervals. The sound is relatively more audible when the engine is cold. The sound can also be heard when the engine is idling but is not as loud. The tuk tuk sound is not audible when the accelerator is pressed with car in neutral but can be heard to some when the engine engine returns to idle. The car otherwise runs fine, uses no oil, produces no smoke and the sound cant be heard when the car is in gear. .
I do know that it is not tappet noise. and nothing on the engine is loose. Any ideas of what it could be? has other honda owners experienced something similar ?