Related Clues:
- Off-the-wall answer?
- It's monitored by an air traffic controller
- Cavern sound
- Attention-getter in the control tower
- Tiny bump on a graph
- Sound heard in a cave
- Delta follower
- Bounceback
- Off-the-wall response?
- Comeback of a sort
- Chamber phenomenon
- Yodeler's feedback
- Alpine reverberation
- Air traffic controller's concern
- Off-the-wall answer