Hey there Craig,
To change the waiting message, go into the Mibew control panel and click on Localize. You will see one there called chat.wait. Once you change the text for that attribute, it will appear to the visitors upon initiating a chat. In regards to the constant notifications, the code is in common.js for the chat sound. I dont know javascript very well, so I am not sure if you can designate that a sound loops through that code. I will check with Ed to see if it is possible.