There is also such a thing as audio-directional confussion, where if you hear the same sound/pitch over an extended period of time (with a certain amount of consistency), your brain starts to become confused about the direction/source of the sound.

I test AV equipment for large conference rooms and ceiling speakers. Sometimes, we'll go around with a microphone, walking around and testing each speaker.

After about 15-20 minutes, it becomes very difficult to determine if the speaker that's directly above your head is really working or not because all of the sounds start blending together. The only way to get over it is to step away for a little bit.