I just went there and my popup blocker blocked 3 ads, I would not be surprised if some might have been audio. Many of the major websites like that have short movie trailers that start without you clicking on them also which might be what you are hearing. I've seen them at MLB.com, Nascar.com, Pepsi.com, etc. I can't be positive but I would not be surprised if what you are hearing is normal.
Ive noticed recently several "audio" ads that come thru my speakers when I visit seemingly innocuous sites like ESPN.com. Even when I don't click on any of the site's ads, these annoying ads continue.
I use spybot, have a firewall and an anti-virus software.