If the engine has quieted down since that video was taken, then perhaps it was just due to the lifters not being "pumped-up" yet. If however it still sounds the same, then there is a problem. These are hydraulic lifters and there should be zero lash. This means there should never be any space between a lifter, a push-rod, the rocker arm or a valve. Matter of fact, there should be about .090" pre-load on the "self adjusting" piston inside the lifter. If the lifter is at the base of a lobe and you can move/rattle a rocker arm by hand (in it's normal direction of travel), then there is too much slack and something should be done to correct it.

When I said possible machining error I was refering to things like decking the block, shaving the head, grinding valves, etc. If the camshaft is new, then it's very unlikely it's defective (it's almost unheard of to see machining errors on these type parts). Still if you have excessive valve noise, part of the troubleshooting process is to rule things out. Cam lobe condition and lift can be checked with engine assembled if you have the proper instruments. If you don't have these things they can be picked up on Amazon and eBay for a reasonable cost (your time is likely the bigger investment). I use a dial indicator with a long extension. I have a mount bracket I made to bolt the mounting arm to the engine and it can be adjusted into place for each lifter. Specs for the camshaft are in the service manual. Tim