Tha author of the threats is the Islamist group "Hizbul Islam".

Rock, rap and love songs once filled the airwaves in Somalia's war-torn capital, one of the few pleasures residents had. But Islamist militants ordered music off the air Tuesday, labeling it un-Islamic in a hardline edict reminiscent of the Taliban.
Stations immediately complied, fearful that disc jockeys would face the harsh punishment militants mete out here: amputations and stonings. The edict is the latest unpopular order from the Islamists, who also have banned bras, musical ringtones and movies.
More than a dozen radio stations complied with the order by the militant group Hizbul Islam, the National Union of Somali Journalists said.
"Journalists working in these stations have in the past witnessed broad daylight assassination of their colleagues and have now been signaled that they would follow the same fate if they do not obey these oppressive orders," said the union's secretary-general, Omar Faruk Osman.

The radio stations broadcasted sounds of animals, waves and gunfire instead of music.