any belt with teeth pulled even slightly tight will sing, may it be a blower belt or timing belt, and it doesnt even have to be very tight to sing. the noise comes from the belt traveling at moderate to fast speeds and the teeth pulling out of the pulley groove, as the belt tooth comes out of the groove, the air tries to rush in to fill the gap, if it happens fast the air crashes into the groove in the pulley and makes a pop sound, and the faster the belt goes around the higher the pitch of the sound