I just installed new hydraulic tappet set due to noisy old hydraulic tappets. 90% noise(tik-tik) is gone. 30-40 kilometres are done after new hydraulics installation but still 10% tik tik noise can be heard. So how to make engine less noisy after getting hot ? Push rod, cam gear, cam sleevee, Hydraulic tappet whole set changed recently.
Tappet noise is a "feature" provided by RE on Classic 350. While it doesn't do any harm as such, you can get the tappet rods set changed (the ones on Himalayan seem to be better : these are lengthier and have a groove). Tappet noise doesn't get better with the mileage. It gets better only with tappet rod adjustments AFAIK.