Next time I hear that sound, I'll check if it's coming from the same spot.
If it's just a tick, tick, tick, sound, that'll be fuel injection most likely.
If it sounds like a soft snare drum roll/sewing machine... Then welcome to the club of not knowing what the heck it is!
All I know is, lately I've been very careful to not punch it until the engine is completely warmed up, and ignoring the sounds as I can't really hear them once warmed up.
As long as I don't hear that awful diesel and racket that was definitely coming from the passenger side of the engine, I'm ok
Now it's right up top, so that piece you spotted might be it.
Let me know if you find out anything!