When standing in a house we hear lots of constant mob noises.  Mainly baby zombies.  At one point there was a repeated noise that sounded like a baby witch.  It kind of sounds like a lot of sped up mob sounds.  We have searched the surrounding area and can't find the source (except for a zombie villager, which we hear occasionally).  We may be overlooking a mob, but with the quantity of noises it seems hard to miss.