I went to another shop today. Chain car shop. Expensive pricks, but usually do good work.
You wont believe what happened... or rather, what the cause of the noise was. ... The spark plug was lose.. 0.o
I told them to bring me out and show me what ever it was they find. I wanted to see it personally. The top of the engine (from our perspective) that has the four connections for the spark plugs.. the middle right one (second in from the right) was shaking/vibrating in perfect rythem with the noise that you hear. When you place your hand on it and feel it, you could feel it in rythem. So they took it out to make sure it was ok. Put it back in and tightened it. And the sound was gone! Everything sounds normal now.

All this damn worry over the last few months. Fear of destroying my engine. Trying not to use the car until this was figured out... and it seems to be the spark plug'
$175 for hour labor fee... which im not thrilled about. Not at all. But having the issue seemingly solved, and knowing my engine isnt going to explode in my face.. that part makes me happy'

Edit: Last time the spark plugs were replaced, as best as i recall, was november 2021. But the car was at 125,582 miles. So 3 years, 7 months but only about 10k miles since then.

I do wonder how it became lose tho. I also wonder why only 1 of the four became lose.