M113 Lifter Noise?

[jcoop]

I have a 2004 E500 4-matic wagon with roughly 120,000 on the odometer. It runs incredibly smooth and starts easy like it should. However, it produces a noise that is certainly not typical or characteristic; it has a tapping sound, almost like a quiet diesel. I took a video: https://www.youtube.com/watch?v=h1QA3LKQaL8

I read that the M113 'E50' 5.0L V8's have a recurring problem with lifter clatter. I suspect one of the lifters has gone bad, reuslting in this sound... any thoughts?

-As a sidenote, I did take the accessory belt off and ran the engine briefly and the noise is still there-