[horndoctor]

This may have something to do with a power management setting. When you get a message the device has to wake up a little before it plays the new message tone. I would suggest changing the notification tone to a longer one. This may help. This has happened to me every once and a while but not always. I have mine set to vibrate on this notification regardless and that def helps to get my attention. You could try disabling some of the power management settings in the registry one by one and see if any have an effect but you may notice a negative effect on battery life.