<unk> , or groaning during sleep, is a parasomnia distinct from somniloquy (talking during sleep). The sound is produced during exhalation as opposed to snoring which occurs during inhalation. It is usually not noticed by the person producing the sound but can be disturbing to sleep partners. There appears to be no physical cause and is not exclusive to dreaming or REM sleep.
Catathrenia
Hyperprolactinemia
Paroxysmal hypertension
Hypoaldosteronism
Acromegaly
Amusia
Dexamethasone sensitive hypertension
Hyperpituitarism