wish to play a sound once in a page to notify of change

I would like to have the pc beep or something to notify the user that that something has changed in the browser which is refreshing every 30 seconds or so.

Hello,
If you're refreshing the page every 30 seconds, I must try to understand you're using some client side languages?

What you could do to notify upon changes, is to have a AJAX request send the change, which is saved in a database, then upon refresh, and/or a possible callback function with the client side request then display or show that the changes have been made.

Obviously you'll need a server side script/class to process the ajax requests and to output the relavant html detumined on any changes made.

Hope this helps,
Shaun