Guys and gals, don't try this experiment at home! You wouldn't want to run 120V household electricity in your ears! Just kidding, but please just don't try it at any voltage levels!
"Interest in stimulating hearing with electricity began with Count Volta in the 18th century. Volta, an Italian physicist who developed the electric battery, connected batteries [approximately 50V] to two metal rods that he inserted in his ears. In 1800 he described that when the circuit was completed he received a 'jolt in the head' and then a sound 'a kind of crackling, jerking or bubbling as if some dough or thick stuff was boiling' (Epstein:1989: 34). Not surprisingly, Volta found that it was quite uncomfortable and did not repeat the experiment too often!
Fifty years after Volta, a Frenchman, Duchenne of Boulogne, tried using an alternating current to stimulate his hearing and heard what he described as a sound like an insect trapped between a glass pane and a curtain."
Source: powerhouse museum