I'm sorry if it's been discussed already, as I can't find a way to search in the thread. My Siri (on PB3) still doesn't play the Listening sound, even though it's said that it should. Also, when I ask Siri for information on anything, and not an action, it will display the information for a few seconds, then close back to the lock screen, making it darn hard to use for many things (including things like finding people via Find My Friends, as it closes before a location is pinpointed.)
If by "listening sound" you mean the two dings or whatever. That's been taken out if you use the home button to activate (to be less obtrusive to people while out in public.) It only plays the sound if you use headphones/Bluetooth speakers or "hey Siri".
As for it quickly closing on you. No clue on thy as I've never seen that happen for me.