This help article lists the most common issues one can face when using the RadNotification control and offers possible solutions for them.
There are three ways to avoid this behavior:
Use the standard ASP:ScriptManager control instead
Set the EnableScriptCombine property of the RadScriptManager to false
disable the script evaluation for the RadXmlHttpPanel in the Sys.Application.Load event, e.g.
$find("<%=RadNotification1.ClientID %>")._xmlPanel.set_enableClientScriptEvaluation(false);. Note that this may cause some issues.
Audio in mobile devices can only be played after a user action. This is a limitation of mobile browsers that also affects the RadNotification control. You can find more information and a possible solution in the Notification Audio Is Not Played In Mobile Devices help article.