When an arrow is fired by a Skeleton underwater and lands downwards on a block, the arrow continuously falls, causing the sound of an arrow hitting a block to repeat quickly and infinitely. Because arrows don't de-spawn when they are moving the arrow never disappears, even upon re-loading the game. The only way to stop it is to place a block on-top, as removing a block just transfers the bug to the block below. 

Even when covering the arrow up with a block, if then removed, the arrow continues again.

There are even situations where the visual of the arrow has despawned, but the sound has not, and in this situation you cannot cover the block as you cannot find it, and the glitch becomes infuriating. 

Screenshot shows arrow 'wobbling' in place as it has landed downwards onto a block. The block beneath has been destroyed and still the sound, animation continued. This screenshot was take after 5-10 reloads of the game.