It is the app, I had the same problem with the messenger app. I had to always have my phone on silent if I was using the app, however once I switched to CM6 I no longer have this problem, so unistall the app, or upgrade to Cm6.
Agree..it is obviously the app. So you will need to root your phone, install CWM, and upgrade to CM6/7 to get rid of this problem, or get rid of the App.
Funny how you said earlier that it was stock, and we asked you what apps you have installed and you said nothing. Now you have recieved a new ascend, and you admit you installed Apps, and are now aware of what app is causing the problem.