What is this Sound (Video)
 

The video is below. You can really hear the sound during deceleration. It started all of the sudden the other day on my way to work.
https://youtu.be/fR3fj8Bkk8U

So went over all the valves and and checked the chain. Some of the valves were lose but that is because I set them that way 9 months ago. This sound started 2 days ago. I "tightened" some of the valves and made sure the locking nut was very secure on all valves, then rechecked the clearance again. I then did a visual of the chain and found it to be normal. It was too dark to check the timing but I think that will probably be fine too. I don't feel like I fixed anything. I was looking for a smoking gun when I took the cover off but didn't really see much. With the sound, the engine performance and idle all seem normal there is just a very aggressive knock. Will do a small test ride in the morning to see if the sound comes back.