What do you think might be causing this sound:

http://www.youtube.com/watch?v=s2pEM3fAepw

I adjusted the valves, corrected chain stretch (installed a 4 degree key), played with the rack dampener bolt, and rebuilt injectors with new nozzles. (No, I didn't test or balance them)

This knocking sound just does not go away. It is the same as it was when I first got the car.

The idle is nice and smooth, and I was very impressed when I took it out on the interstate today. it felt powerful and not loud (and I could not hear the bloody knock at 60 mph).

Normal sound?

Should I keep obsessing about it??