Possible Clues:

• Nursery complaint
• With 28-Across, sad trombone sound effect
• Crib note?
• Cry from a nursery
• Cartoon baby's cry
• Infant cry
• Plaintive cry
• When repeated, a guitar effect
• Doubled, a psychedelic guitar effect
• 'Do ___ Diddy Diddy' (1964 hit)