Interesting, that's an innovative use for a digital camera.
I'm not sure how many X20 users you'll find here in the forum, and the reviews sure don't mention "startup noise". :-)
You may want to try asking the question in the Konica-Minolta forum. I don't know if you'll get any responses there either, though. It depends on whether or not an X20 user sees it.
If I were you, I'd just go down to a store and try it out foryourself. Many retailers have demo models setup just for this purpose. Then, you'd be able to compare the noise from your camera, to models you are considering.
Keep in mind, that even ifan X20 user sees and responds to your query, they probably would not have owned both models (Canon S200 and Minolta X20), so they would not know how they compare in this area.