Spoiler Question
If noose like music hurt their ears so bad, why didn't gunfire.
shareAny loud noise confused/distracted the evolved zombies. However, since the music was a sustained and extremely loud noise source; it disoriented them completely while it was on.
That's the reasons they were able to keep a swarm of them from descending on their location for so long. Patrick's radio station being played on blast every night kept them away from the area. Once he started to hear voices from the radio he stopped playing at night. This combined with the fact that the chained up zombie was calling his brethren is what led to the zombie attack on their location.