Aye30 in his post above has a good suggestion. In the day, I used automotive/mechanics stethoscopes to isolate the location of noises, see my post at
Cold start rattle 2012 GD Premium 1.8 auto.
If you haven't got an automotive stethoscope, I recommend getting one (a good brand name) as they are reasonably cheap for what they can do. I'd run the probe of the stethoscope over the more likely culprits e.g. along the "rocker cover" (forgot its modern name
) under the large plastic cover atop of the engine and along the timing chain cover and tensioner. Don't test too many places the first time as it just makes it harder to remember their noises.
With a stethoscope I would: (1) Test with the engine cold, at idle and at slightly increased revs. (2) Test with the engine warmed up (not hot!!), at idle and at slightly increased revs. (3) Test with the engine at operating temperature, at idle and at slightly increased revs.
Hopefully, you should be able to detect the location where the noise starts loud and then quietens down as the engine heats up. Just a thought.