sudo dd if=/dev/sda
the internal PC speaker makes sounds. Also all fonts, even the prompt and typing input has different characters such as "♡" or "•".
If you need to know more, comment please.
What I usually do is of=/dev/null or >>/dev/null for reading performance testing and for spinning up the optical drive (with
count=1 iflag=direct skip=500000), of which I skip to LBA 500000 to put the laser lens in the center of the data part. But I wanted to try out once what happens if I do not redirect the output anywhere, and that happened.
Fun fact: The same happens to Windows too.