Possible Clues:

• It's heard before ''Gesundheit!''
• 8 Down sound
• Sound that triggers 'Gesundheit'
• Tickled nose noise
• Possible reaction from getting a cold shoulder?
• Cause for a blessing?
• 'Gesundheit!' preceder
• Sound from a 45-Across
• Sound preceding 'God bless'
• Gesundheit predecessor