Great point by BD22...
You can change the vibration pattern and customize it to your liking... scroll up in the Text Tone window.
Or you can add a custom ringtone that consists of a single high-pitched "beep", like this:
http://www.soundjay.com/button/sounds/beep-07.mp3
It's unobtrusive, yet you'll acclimate to the sound easily. This is what I've done, but you have to find a short tone that works for
you. YMMV