Board Thread:Episode Discussion/@comment-27431372-20151220003638/@comment-26397825-20151220004456

I don't think it was the noise that the Grimm were attracted by, but rather the large amount of negative feelings the crowd was making. Just after Yang broke Mercury's knee everyone was shock into silence - this shocked and negative feeling towards Yang and the situation would be what is attracting the Grimm. Then as they came to their sense, the negative feeling grew stronger and the crowd started making noise.