This guy in the YT vid below is reviewing LED headlights for his Accord but in the background, listen to the tapping and clacking of the engine in the first 3 minutes; best heard at the 45 sec mark. I hear this exact noise in so many 6th gen 4-cyl engines. Doesn't seem to harm anything, though. My engine has sounded like this for the past 30,000 miles or so despite me being the original owner and maintaining it well. Had the valves adjusted by the dealer a while back without any change. I later isolated the noise to the driver's side of the engine. Perhaps an accessory or something under the timing cover...?

 

Use a stethoscope or long screwdriver to get closer to the sound source.

You could pull the accessory belts (sequentially) while cranking engine and running to see if one of the accessories is causing the noise; AC or PS, or Alternator.

W/ accessory belts removed you should be able to confirm if sound is coming from underneath timing belt cover. Tensioner idler is most likely source of noise. A damaged timing belt is another possibilty. You could also remove upper timing belt cover to get a peek at possible source.

good luck