I have some good news for all PerMa stealth mages:
Over at the Audio Overhaul of Skyrim 2 (AOS) comments thread, some PerMa users have reported getting a permanent looping burning fire sound after a successful sneak attack using magic. After some investigation, I discovered this is caused by one of PerMa's scripts, and actually isn't related to AOS. The reason why AOS users are more likely to notice it is because that AOS makes the sound a little louder and clearer.
Digging a little deeper, I figured out the exact cause in the script itself, and found a way to fix it so the "stuck" looping sound is gone.
T3nd0 has confirmed the issue with the script, and has very kindly given permission for the replacement fix script to be hosted over at the AOS downloads page. You can find the fix script in the Optional Downloads section.
Note that this script will fix the looping sound problem for all PerMa users, even if you don't use AOS.
So, I recommend this to everyone using spells in PerMa until an official fix hopefully comes included in the next PerMa update.
For some more information, please see my read me for the script fix here on pastebin.com.