[cobalt327]

Ok, I can't tell if this is spark knock or timing chain rattling.

EZ- pull a bunch of timing out of it and see if the noise quits!

If it does- timing too advanced initially.

If it doesn't- timing chain might be at fault, but I have to say- it has to be LOOSE (and an OEM-type set-up) to actually hit the inside of the timing cover, IMHO.

If it's the chain, you should be able to get it to do it sitting still, in park, by working the throttle on and off. It's most likely to do it during deceleration.

Be sure the fan's not getting into the shroud, that there's nothing moving around enough to contact any moving part under the hood. I'm definitely thinking it's something besides the timing chain...