Could be the tensioner is loose, guides broke, chain jumped a tooth... not sure but hoping that I find a concrete problem and easy solution. Seems to have been driving fine, but ever since I had the manual in I drove it hard, wheel hopped quite a bit and shifted hard (leading to the cracks/breakages on my turbo manifold) so I think the shock from that also transferred to the timing and might have done something lol.
I've re-used the same tensioner/chain/guides the last 4 times the engine has been apart, which began in 2008.
Damn I tapped things with a rubber mallet and it went away and now I can't make it make the rattle again lol.
When I rotate the crank by hand back and forth I don't hear anything weird from the chain area.
Edit: Pinpointed vibration issue to the warped v-band on my downpipe. Easy fix, next week. Who knows what the other rattle is but I know that this noise is solely from the v-band being warped beyond belief. The air gap is causing some crazy harmonics as the exhaust squeezes out.
Still, curious what this was. Can't reproduce it anymore, just was a random observation that one time.