Deducated Alarm Speaker?

Does the Prius have a dedicated speaker for alarms (such as back-up and seat belt warnings) that is buried up under the dash or are these transmitted through the tweeters in the A pillar?
The reason I ask is because last week I had the VAIS SL2i I-Pod adapter installed. The unit is working out great but I'm getting a shrill squeal at start up now. It only lasts for about 3 seconds but it's really annoying. It happens regardless of what audio mode I'm in, or even if the stereo is turned off.
If there's a dedicated speaker, I'd like to permanently disable it.