Bash Script to Prepend a Single Random Character to All Files In a Folder

I have an audio sample library with thousands of files. I would like to shuffle/randomize the order of these files. Can someone provide me with a bash script/line that would prepend a single random character to all files in a folder (including files in sub-folders). I do not want to prepend a random character to any of the folder names though.

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Example:
Kickdrum73.wav
Kickdrum SUB.wav
Kick808.mp3

Renamed to:
f_Kickdrum73.wav
!_Kickdrum SUB.wav
4_Kick808.mp3

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If possible, I would like to be able to run this script more than once, but on subsequent runs, it just changes the randomly prepended character instead of prepending a new one.

I have been searching the internet and experimenting for some time now without any luck. Thank you in advance if you can help me!