SharePoint 2010 User Control Mouseover JavaScript Sound

I have created a user control for SharePoint 2010. One of the requirements is to play a sound file on mouseover. I have a simple Javascript solution which works in a standard ASP.NET application, but is giving me trouble in SharePoint. The relevant .ascx looks like this:

<div id="divMouse" onmouseover="playclip();" onmouseout="stopclip();">
Content
</div>

<div id="divSound"><bgsound id="sound" loop="false" /></div>

The JavaScript itself is so:

function playclip() {
            document.all['divSound'].src = "/_controltemplates/MyNamespace/MySoundFile.mp3";
    }

Mousing over the div in SharePoint results in the first second or so of the file playing repeatedly, as long as the pointer is in the div. When I place an alert after the above line in the mouseover event, it gets more interesting - if the alert box is left open, the sound file plays to completion. If it is closed, the sound stops instantly - the pointer has to leave the div to click the 'OK' button on the alert box, and the stopclip() code has also been shown to be executing with a second alert box.

I would appreciate anyone's thougts on this, as I am out of ideas, and haven't been able to turn up anything that helps.

Echo Train Nashville TN