Ok, I counted the knocks, and I get 64 knocks (for some reason they are real easy to count in multiples of 8) in 9.6 seconds.

That works out to about 400 knocks a minute. If I am off by about 1/2 second, this is about +/- 20.

The car idles at about 700 - 800 rpm.

Roughly, my knock happens once about two revolutions i.e. once per complete cycle.

So, it could be happening, for example, during power stroke of my #1 cylinder, which could be some looseness in the rod bearing.

Or it could be happening on exhaust stroke at the top, if the ex valve interferes with the piston...

Thoughts?