I mounted a gopro under the hood (to an AC refrigerant line, actually) pointing at the front timing chain cover (the gold color nut is attached to the top of the serpentine belt tensioner; the camera is mounted about a foot behind the passenger headlight pointing in the general direction of the center of the firewall). Anyways, heres the video. https://www.youtube.com/watch?v=ADXb2-9r8zg You can hear the injectors kind of loudly because they are so close (the gopro is literally inches away from the engine); but you can clearly hear the sound I'm chasing at the following time points: 0:12 0:25 0:33-0:59 I intentionally move the throttle slightly around the point where it makes the noise I did also make a video of the motor at idle and revving to 3k-4k both quickly and slowly in park (not moving), but not a single sound was heard so I didn't bother to upload it. I can get a new tensioner locally and throw it in the car tomorrow and see what happens. I guess there could be some kind of resonance combined with how the crank speeds up and slows down every 180 degrees and it's causing the timing gears/cams to somehow rattle against tension/slack in the cam....I've already come this far, might as well throw one more part at it, right?