289 Engine noise w/video

On my computer it's tough to tell but it sounds like rocker arm clatter. But since you've already adjusted the valves I'd say it's safe to say that ain't it. Maybe a lifter? Sure sounds cam or valvetrain related to me.
 
It seems most pronounced on the driver side. If you don't have a stethoscope (cheap at Harbor Freight) use a long screwdriver or breaker bar with the handle or smoothest part pressed up tight to your ear and probe around touching it to various points on valve covers, etc. to help pinpoint the location.
HTH,
Gene
 
Thanks everyone. I took off the transmission inspection plate and everything looks snug. I am going to revisit the valve train on the drivers side. I'll post after I take a better look.
 

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