PMsound plays a sound when you receive a PM. You can set the volume with the setvol command.

ChSound monitors one channel and plays a sound whenever someone chats to it while that channel is not your active channel. You can change the monitored channel in-game with the setch command (help channel by default). setvol works here too.

I whipped up a quick synthesized sound for both plugins so that they work off the bat, but I recommend replacing it with your own sound file.

PMsound v0.2 --UPDATE: PMsound v1.0
ChSound v0.2 --UPDATE: ChSound v1.0

Updated: now saves settings between sessions to the config file. Also added a test command to check the volume settings.