If it was raining, perhaps the clonk noises are a drip on a windowsill.
VolUpInt doesn't sound to me as if it reduces to silence toward the end. It's got a bit of the same flickery sound of the gain changing that VolumeNormInt has, but otherwise the only sound is a bit of bumping at about 21 seconds which sounds like someone moving around, perhaps in another room.
You may have an older version of Cyberlink Youcam. It appears to be available now for purchase or as a time limited free trial of version 5.
If js reports rain in the background, this clonking may well have occurred that way, but the silence at 21 seconds and the crackle thereafter, would not have occurred.
Another theory is, if js puts some kind of lock (seal) on his recordings, it is possible that the spirits cannot break through this seal with (attempted) speech, but they can cause a clonking, an interference, a silence, to still have their presence known.
