Noise Marines

Noise Marines are superhuman soldiers/traitor marines who have deeply dedicated themselves to the Chaos God Slaanesh. They form the backbone of the Emperor's Children traitor legion and can primarily be found there, but they also exist in Slaaneshi warbands such as the Flawless Host. They make heavy use of powerful sonic weaponry, more than any other known faction in Warhammer 40k.

History
The first creation of Noise Marines goes back to the days immediately preceding the Horus Heresy. After the Cleansing of Laeren introduced corruption into the heart of the 28th Expedition Fleet, noted remembrancer BequaKynska eventually produced a grand symphony she called the Maraviglia, at whose debut (and only) performance were present several Emperor's Children space marines, including it's Primarch Fulgrim. This performance, inspired and entwined with Slaaneshi powers, not only caused the abrupt daemonic possession of several of the orchestra, but also spurred the audience to engage in an orgy of sex and violence alike. During the "performance" it was noted that the musical instruments were able to produce effects variously disorientating, stimulating and downright murderous. Not long afterwards, during the infamous Battle of Isstvan V, some Emperor's Children marines took to the field armed with these weapons, becoming the first Noise Marines. During the Heresy, these early Noise Marines developed powerful but dangerous psycho-sonic weapons known as Kakoponi.

After the Heresy, the early Noise Marines took their deviant behavior to a new level with their new patron Chaos God and over the years of bloody warfare have honed their bodies into sensory extremes where nothing can stir their emotions other than the din of battle and screams of the dying. The louder the noise or sensation the greater mental reaction a Noise Marine achieves, and on the battlefield he essentially ceases being human but rather becomes a receptacle for the sounds of agony and death.

Wargear
Noise Marines (as the name implies) make heavy use of their trademark sonic weapons. As standard noise marines are initially armed with a bolter, but the majority of noise marines will typically switch out the bolter for a sonic blaster.
 * Bolter A semi-automatic 75.cal assault rifle which shoots miniature rockets that are designed to explode after penetration, ensuring full lethality.
 * Sonic Blaster This weapon produces waves of devastating sounds which can violently shake and rip it's targets apart. It can be used to produce either a continuous sound or many shorter pulses.
 * Blastmaster This weapon produces a throbbing bass note which is strong enough to burst eyeballs and rupture organs. At different frequencies the weapon can have different effects, from harming individuals with a varying frequency to destroying an entire area with a single pulsing frequency.