Friend of mine asked me about this knock. Im thinking pulley or engine mount. Thoughts?
Yup, that is a knock. Can’t tell where it is coming from. It is hard enought to locate when you are standing over it, impossible with a YouTube video. Sorry.
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Fair enough. Thought id give it a shot. All i have is the video too 
Update: she says you mainly hear it when car is cold not warmed up
You might try using a length of old garden hose as a sort of stethoscope to narrow down where the sound is loudest. For best help here, suggest to post make/model/year/engine/transmission.
193699 '05 Acura mdx
Im gonna use my stethoscopes when she arrives
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Well it kinda sounds like a pulley bearing knock except it’s not constant. Sorry to say it also sounds like the timing chain may be knocking against the front cover. You can take a hose or stethoscope or something to try and localize it. I had one mechanic listen to mine and couldn’t tell so don’t feel bad.
Theres some scraping on a lower pully when using a stethoscope. But surely that wouldnt go away when warm?
Well that’s good news.
After getting the car I didnt get to hear it because it was warm, but im thinking ita the water pump. Using a stethoscope on its pully all I hear is metal grinding.
If the noise is not obvious when you check it out… With the engine cold, remove the serp belt and see if the noise goes away or still there, that will tell you if it is a serp belt driven noise or not… If the noise goes away, put the belt back on and try again just to make sure it was not a one time quiet thing…
Unfortunately as Tester pointed out, that trick doesn’t work on a timing belt driven water pump… lol
Never mind.
Right. My game plan for the morning was to do the belt trick. Got me stethoscope ready. Seems to be an awefully deep knock for a timing belt rather than a whine, but using the steth on the water pump w out the knock all i heard was grinding on the nut. So. Maybe
Found out it was the harmonic balancer
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Glad you got it properly diagnosed. On some engine configurations the harmonic balancer can be involved in the spark timing; just a head’s up in case there’s any indication of an ignition timing problem. .
I’d heard scraping noises coming from my truck’s water pump, 302 Ford V8 engine, so such a thing is possible. It has always been caused by calcium deposits from the cooling system accumulating in the water pump, and usually means the water pump will be failing soon. A good water pump however does make a sort of whirring sound when listened to w/a stethoscope, and that could be confused with a slight grinding sound.
She does have a rough idle but her misfires are 0 on all 6 cylinders per my obd2 live data. Her IAC failed its test so probably that. But her rpm idle is 750 so she also uses the wrong gas which could cause that