Strange Chime Noise WSSS Feed

[philip]

Every so often on i think it's when it gets to the radar frequency there is a weird chime in the back ground as if it was an email notification which keeps doing it every 2 seconds if it was to stay on that controller.
http://www.liveatc.net/flisten.php?mount=wsss2&icao=wsss

[757-rules]

I have listended a couple of times, but didn't hear it...

[datainmotion]

I hear it - deep in the background. I believe that is a notification sound in the cockpits we're hearing (maybe a marker?)