Diagnosing Engine Noise

I've got an 05' w/ a 4.0L @ 272,000km that has all of a sudden developed a slapping/tapping noise from the engine. No significant event leading up to the start of the noise. Here are some details I've noted thus far:

Short Google Drive video clip for reference-> https://bit.ly/3fVC953

• Coming from the driver-side front of the engine
• No codes or check engine light
• Stethoscope shows sound is not coming from under the valve covers. The sound seems strongest when scoping against the timing cover
• Timing chain tensioner is only showing one ring worth of extension
• Chain didn't have abnormal slack 6 months ago when the valve cover seals were replaced. The sound was not present at that time
• Very little sludge in the valve train
• Tapping increases in frequency and smooths out as throttle is applied
• Engine runs smoothly with no abnormal vibrations
• Doesn't seem to be down on power or fuel economy
• No carnage was found during the oil change yesterday
• Accessory belt is in good shape and has less than 5000km on it
• Fan blades are not damaged nor is any of the shrouding

I am leaning toward an issue with the driver's side chain guide. Any thoughts?

 

Look up what an exhaust manifold leak sounds like.
Edit: Is that your video or something that sounds similar you found?

 

Video I took earlier today. I would have thought that an exhaust manifold leak would have been a much more rapid tapping sound. I guess the same could be said for anything timing chain related as well given the rate at which it is rotating.

 

That video sounds like a bearing possibly. Or something is wrong with the pulley.

 

I'll try pulling the drive belt off tomorrow and briefly running the engine.

 

Could be rotational related so I would rule out external things first so pull the serpentine fanbelt and start it for a very short listen and if no noise start looking at all the other stuff under the belt.
With the belt off spin everything and listen and also feel for bad /loose bearings on pulleys, tensioner, water pump, AC, PS, Alt. As an 05 there has to be lots of wear on things.
I would do before starting to go inside the engine and all the effort/dollars just to be sure it's really internal.

I was writing this as you were also thinking the same thing !!