WoWDB

This item was only available to players during Patch 5.3.  Edit:  The toy is once again available in the Legion expansion.  It is only sold by a Horde-aligned NPC.

Sen'jin Spirit Drum is actually three bass-type drums in different sizes and sound.  (The actual name when you mouse over the summoned drums is Bom'bay's Spirit Drum.)

The left, smallest drum creates the highest pitch of the three when right-clicked.  The middle drum creates a sound about half an octave lower.  The right, biggest drum creates a sound about a half-octave lower than the middle drum.  Only the player who summoned the spirit drum may hear the sounds they create, though anyone can interact with the drums.

The spirit drum lasts for 30 seconds before fading away.

In Warlords of Draenor, this item will be added to the new Toy Box feature and no longer take up space in a character's inventory.  You will be able to "use" the item straight from the Toy Box interface.  The Toy Box will be account-wide and therefore so will this item.