Hello! Pleasure to meet you all and thanks for checking out my thread.

My 99 e320 is running flawlessly, haven't had a dash light or issue aside from oil changes for a couple years. Holds a steady idle and was just considering doing motor mounts.

Until I noticed this noise:

https://youtu.be/5xNU_h6itbs

It is very noticeable with the cover off the motor and I can't quite pin down what it is with my mechanic's stethoscope. I've seen many threads with identical sound clips but didn't see any exact conclusion on what causes it.

I've read speculation that it's timing chain, tensioner, oil pump, lifters, that is is an emergency, it's good for 50k miles, etc. Please help me narrow the list.