Oh, I just remembered how I had a high-pitched noise (15 kHz I think) saved on my phone and once I played it in class(I was about 11 back then), annoyed the hell out of my classmates, but the teacher had no clue.<br>Edit: just checked the previous video, heard the noise, but had to focus on picking it up and increase the volume in my headphones, else it was barely, if at all, noticeable.