According to the video uploader, the noise came from frogs outside the chapel. When using the on-camera mic, it's hard to isolate just one sound source as the mic has a wide pickup pattern.

Getting rid of the noise on a computer can be troublesome as well, as certain frequencies overlap with Fr.'s voice and would make his speech hard to understand. Aside from a lavalier or shotgun microphone, or killing the frogs :ready-to-eat:, it's hard to get clean audio in that type of environment.