Chakchak Ghost

This is a yokai I just learned about. It's called the 'HweHwe Ghost' because it makes a 'hwe hwe' sound, and the 'Chakchak Ghost' because it makes a 'chak chak' sound. There are records that vengeful spirits of those who died during wartime became ghosts, causing sleep paralysis in people and even invading palaces to cause disturbances. It's said to have no physical form, only making sounds to torment people.