I think that an option to disable the PM Alert Noise should be an option that could be changed in the Player Settings "/ps". This would be a great feature for people that have friends that constantly spam you... It get's annoying when all you hear is. "Ding!" "Ding!" "Ding!" especially when your pvping or doing something that takes focus. And maybe with the Option of disabling the PM Attention Noise, how about the Option to change your PM Attention Noise! Hopefully this Suggestion will be considered.
I believe this would be VERY easy to add. From my very basic coding experience, you could just have an integer (or whatever) and when you turn on PM noises it goes to 1 and off it is 0. Then in the PM code before the dinging noise make an if statement saying "if (Noise == 1){ player.playSound(player.getLocation(), Sound.LEVEL_UP, 5, 5); }" (I got the sound from Aikar's post on chickeneer's profile)
Done, will go out next deploy (ability to turn it off). We can't do too much with the sound at this time.