Do you have your notifications set for on? It might be beeping for an incoming mail or an app that needs attention. Or it could be that you are missing someone iMessages, etc.
Check your apps to see if there any red circles in it's corner. It is telling you it needs attention.
Addendum: by the way, I deleted a duplicate thread that you created. Please avoid doing this since this makes it difficult for other members to follow and potentially help you out. It is also against the Forum Rules.
http://www.ipadforums.net/forum-rules-help-info/2119-forum-rules-everybody-please-read.html