Sound asleep?
Else clues• Alphabetically last entry in the Official Scrabble Players Dictionary
• Interjection that's the last entry in the Official Scrabble Players Dictionary (it requires both blanks)
• Nighttime noise
• Sign of sleep
• Snoring sound
• Snoring, in comics
• Sound of sawing logs?
• Sound of sawing wood?
• Sound of snoring
• Sounds from Dagwood