I heard the noise on your video - sounds to me like a noisy valve lifter. When they start losing pressure, it takes awhile for them to 'pump-up' with oil after startup, but even when they quiet down from that, you still hear the noise because the seals are not really holding oil pressure, and it's slapping the valve. Doesn't cause immediate damage, but the fix here is to replace the lifter(s). A blown lifter could potentially cause a valve issue down the road though, so I would put it high on the list.