See this script. I tried the exactly what you wanted.

#!/bin/bash



for item in *.mp3

do

    mv "$item" "$(cat /dev/urandom | tr -cd 'a-z' | head -c 1) $item"

done

How does random letters picked up

Here I am picking up strings from /dev/urandom and deleting all the characters which are not in between [a-z] and at last keeping only the first letter.

How to use

Copy the code to a file, say rename_song.sh, give it execution permission using terminal as follows,

chmod +x /path/to/rename_song.sh

Copy rename_song.sh to the directory where you have .mp3 files. run the script from terminal (first navigate to the directory where you have .mp3 files) as,

./rename_song.sh

If you have a list of files like

song.mp3    song1.mp3    song2.mp3

song3.mp3   song4.mp3    song5.mp3

They will be renamed like this:

a song.mp3    g song1.mp3    k song2.mp3

r song3.mp3   P song4.mp3    A song5.mp3

If you want letter as well as number then replace tr -cd 'a-z' by tr -cd 'a-z0-9', and it is always better to use a simple shell glob instead of parsing the output of ls.