When all the birds are gone to sleep, and all the frogs are still, then you would hear the fairy pipes come out upon the hill.
13 seconds sound clip from The Danny Kaye Radio Show - "A Baby From Washington" (3.02.1945).
You can hear this line at 00:07:37 in the radio play.
Quote context
[...]
- I don't know, but it should have been Lucresia Quivertonsil or Natalie No-throat or something.
- Wasn't there anything good about her?
- Coax me.
- Come out! come out! Listen on the air! Up there! down there! Fairies everywhere!
- Oh hark! Oh hear! Can't you hear the tune? Airy fairy pipers underneath the merry moon!
- Come out! come out! Listen on the air! Up there! down there! Fairies everywhere! (2)
- Oh hark! Oh hear! Can't you hear the tune?
[...]