Make sure everything is tight.
When I 1st started my car after my rebuild, everything was cool, then all of a sudden I got this SUPER LOUD NASTY KNOCK, and I was like WTF?? Took the front cam cover off, and turns out the cam gears werent tight, so they were hittin the cover.
Does it sound like popcorn? OR marbles in a can? If so, it could be detonation, which is also bad. Using 93 octane? Hope its not rod-knock, good luck with it.