Although the viscosity curves of SAE 30 and 40 oils are very close at 80C there is a considerable tolerance allowed in the SAE standards. Mobil 1 is at the "thinnner" end of tolerance than other oils. It may be that this has affected the way the hydraulic tappets pump up.
Also if you haven't done the mileage for an oil change in 2 years then I would say you are a low mileage user and this should be classed as arduous conditions. You should follow HJs advice and change the oil at least once per year, preferably twice.
My suggestion is that in the first instance you take the car to a trusted local mechanic and have a oil change with proper flush carried out (by which I mean using flush oil not additive followed by a short flush with half the correct engine oil using a new filter for the flushes). Make sure you use a good quality oil of the correct grade (5W30 - there's plenty of good oils of this grade).
Any issues with the timing chain and/or tensioner are IMO most likely due to the lack of care than the Mobil 1, evn if it's the Mobil 1 that's brought any issues to light.
If after an oil change the noise persists, take the car to an old school mechanic who can listen to the noise to identify potential cause and can then inspect to confirm.
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