Sound does not come from one ear plug but does from another ear plug.

Have you tried to use them in another device?

Same Problem? If so, under warranty? Contact Beats for replacement. If not, then have you tried a different headset/ear buds on the same device? The idea is to determine if it is the device your listening to or is it the ear buds.

Those are too difficult to repair by the average user. The issue could be the ear bud, the wiring, the control board (volume/mute) or the connector. If they are not under warranty, it would be more cost effective to just replace them.