The Choir is sound. Well, maybe. It can manipulate sound, I know that. It can change what you hear. It can turn a "How are you?" into a "I hate you." It can turn a nice song into endless screaming.
It can turn your brain into a pile of mush. Yeah.
There are several limitations to the Choir, if you ever encounter it. One: in order to manipulate sound, there actually has to be, well, sound. Noise. Talking. Without sound, it probably won't do anything. (Of course, since an area being completely soundless is almost impossible, I'll let someone else try test this out.)
The other limitation is on a variation of the Choir: sometimes during an encounter, a grey mold is seen on the walls, ceiling, or floor. This mold is often thought of to be the Choir. If you could, say, destroy the mold (preferably with fire), you could get rid of the Choir in that area.
There are two problems with this method, however: not every appearance by the Choir has the mold. This either means that the mold isn't the Choir and might be some byproduct or that the mold is simply one aspect of the Choir. If it's the second case, you can still burn it - but be careful, because it will probably resist and turn the sound of your flamethrower into a screeching noise that will make your ears bleed.