OK, so I finally listened to the video. That has to be a bent push rod.

I don't know what these cost but it might be time to throw in a fresh set of them. I know that means a lot of work but it also means that you will find one of these that has flattened out on one or both ends or is bent. It does not take much of a bend to get a sound like this.

A good way to find a bent push rod is to stop the engine and then turn it over by hand. At some point each rod will have enough slack to be turned by hand and when you start to twirl them around any push rod that is no longer true will be easy to spot as it wobbles in your fingers.

Then you could just remove the adjusting screw from the rocker arm, push the rocker over and pull that rod out and replace it with a new one.

If that kills the noise then plan on doing all of the push rods since they will all be just a little more worn than they should be. When one of them finally fails the others are not far behind.