Related Clues:

• Compete on ''American Idol''
• High air?
• .Speak in a trembling voice
• Sing in high pitch like Swiss mountain dwellers
• Sing falsetto like Swiss mountain people
• Sing in high trilling tone like Swiss mountaineer
• Sing like Swiss mountain dwellers
• Make melodious sounds with voice
• Vocalise musically
• This might make one's plea nice and sound
• A sentence might get one at the double there to make 28 across
• Do this twice and it may get you to jail
• At last this led one back to Switzerland, by the sound of it
• Just one short invoice, perhaps
• Note that this is unsteady enough to make one less crotchety, perhaps