Skinny Puppy found out their music was blasted out at the detention center in southern Cuba from a former guard who is a fan of the band, keyboardist Cevin Key told Canada's CTV Television.
Rights groups say that prison officials subjected Guantanamo's terror suspects to "deafening loud music," often featuring violent lyrics, during interrogation.
Several other bands, including REM, Rage Against the Machine and Metallica have denounced the use of their music at Guantanamo.
The amount they requested may be a reference to 666, known as "the devil's number", in light of the band's Gothic themes.
The group, which has a cult following, has performed live with band members smeared in fake blood, sporting machetes, animal skins and heavy black and white makeup. They have even included mock executions in their performances.
Key said band members were "offended" to learn the claims that their music was played at Guantanamo to "inflict damage" on detainees.
