Thanks! That worked great, it now terminates cleanly, and music on hold sounds better too! I originally followed the instructions at voip-info.org/wiki-Asterisk+ … nhold.conf , but missed the mode=files part, and assumed they needed to be mp3!
Anyway, just incase there is someone else that missed it too, here is what I did to change to wav.
I converted the mp3 music files to wav format and stored them in a new created directory called /var/lib/asterisk/mohwav.
mpg123 -s --rate 44100 --mono /src/mp3/fpm-calm-river.mp3 > fpm-calm-river.raw
sox -r 44100 -w -s -c 1 fpm-calm-river.raw -r 8000 -c 1 fpm-calm-river.wav
I then updated /etc/asterisk/musiconhold.conf as follows.