The GI article states that some spells and dragon shouts will be spoken in a whisper, like invisibility. Having to shout at the top of your lungs would kind of negate the purpose of a stealthy spell.
Hehe, I can see it happening. Totally breaking immersion. Although other checks are probably in place against AI, I would like interior doors to produce noise level according to your stealth mode and skill as well. So it at least sounds that you're trying