What’s the best way to tell if a stethoscope is inconclusive?

Here is a video at hot idle:

https://youtu.be/JtOzRnUv79s

It’s the tapping noise that only seems to happen at just off idle. It’s most pronounced then. After a few more RPMs, the oil pressure pegs and it isn’t audible. But the fuel is also flowing more.

Any thoughts on the tapping/ticking sound? I’m willing to proactively pull the injectors and do a pop and balance job on them, but I’m also willing to pull the cam and swap lifters. I need a new VC gasket anyway on this new to me car.

Drives and runs beautifully, has some dragging brake issue but otherwise really great. But this tapping is noticeable much more than other cars I own including higher mileage 602 engines.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)