Dr. Mario (NES)

UFO sound glitch

First, trigger the UFO ending by clearing level 20 on "hi" speed. If you press Start to return to the game while the UFO sound is playing, the UFO noise will keep looping in the background, preventing some of the music and sound effects from playing. The noise will keep going as long as you keep clearing levels, but you can stop it by waiting a short while on the Game Over or Stage Clear screens, or by returning to the menu after a game over.

Found by: The Chef

YouTube video:

Emulator video files