snapping

[no limit]

lately my ex is making this wierd snapping noise under load. i thought it might be the timing chain so i checked it and the adjuster and they both seem fine, the chain is snug and the adjuster mover back and forth like its supposed too, i also checked the came sproket and it is lined up like its supposed to be, ive adjusted the valves several times and it still does, when the engine is cold it is barely noticeable but as it heats up its really loud. is it possible for the chain to jump a tooth on the lower sproket(crank) cause it to be out of time?

any ideas what would cause this?