Marvel Mystery Oil
If it's not an exhaust leak it could be timing chain tensioner. You could try some Mystery Marvel oil to see if it's dirty lifters.
might help, probably won't hurt. I know people who have used it in the past as a "flush" before an oil change, with mixed results, but nothing horribly bad has happened. It does sometimes "fix" clicking/sticking lifters. There's nothing particularly harmful in that product, according to the SDS at http://www.marvelmysteryoil.com/sds/
if you use it as a "5 minute flush" before an oil change. It can dissolve some sludge/gunk and get it to flow out with the used oil.
I also like Motor Medic "Motor Flush" https://www.motormedic.com/motorflush
as a flush before an oil change. Again, it can clear some sludge and gunk out of an engine, and it can stop ticking lifters (sometimes). there's nothing in the SDS https://www.myniteo.com/Catalog/MSDS...e=SDS_US_GHS_E
that would be harmful or bad for your engine when used as directed.
Either of those products can also clean "sludge" and "gunk" out of old cracked seals and expose existing leaks, so be careful and evaluate your risks and potential benefits. A horribly leaking rear main seal isn't "better than" a stuck/noisy lifter.
Note that other products that are sometimes used for this contain alcohols (methanol and isopropanol are common) and are not recommended to put in your engine at all. Those products can actually damage things. Stay away from anything that contains alcohol of any kind, or anything with "snake oil"<<<<<<<<<<< err, "proprietary hydrocarbon blends." Check the SDS for anything you pour in your crankcase or fuel tank, and if you're not sure it's harmless, don't pour it in.