When people hear a recorded phrase looped numerous times, they begin to hear it as a song.

If you’ve wasted enough time on YouTube, you know this all too well. It was first discovered by Diana Deutsch in 1995, when she was fine tuning a commentary. She noticed the phrase “sometimes behave so strangely,” which was on a loop, started to sound like it was being sung instead of spoken. 

It was later investigated further in 2008 and 2011. Three groups of subjects listened to a sentence and then ten presentations of a few words out of that sentence. The listeners judged whether they heard the phrase as speech or like a song. In all cases, the listeners thought it sounded a bit like a song. 

The interesting thing is that for this phenomenon to occur, the phrase has to be repeated exactly the same over and over- if there’s any variation, the brain just perceives it as words. This was further proven when listeners reproduced what they were hearing: they all repeated the words in a way that sounded more like a song. This could go a long way to explaining many of those videos out there on Youtube. 

(Source)