'ding' notification sound when receiving a tell
 

I don't remember this being part of classic, but is there any way to set this up?

Would be very helpful to field messages while afk

There is an audio trigger section under options. You can have different sounds for all sorts of text appearing on your screen.

Sorry, I don't see any audio triggers when I press Alt-O.

I am using Velious UI.

Load up the default UI, right click on the EQ button, and there will be an audio triggers window accessable through the Actions category if I recall correctly.

you can also go to key bindings, and map the audio trigger window to something like say shift+T, to toggle the window on and off as needed.