I reported this to Michael at WebFlyer last week and he is looking into it. It is one of the ads. From my post in the Netscape hanging problem thread:
First, the pop ad at the bottom of a typical FlyerTalk page that now has the annoying sound file. I got it again today. It is an ad for "netstocks.com." It is NOT a normal animated GIF. I went to right click on the ad to get the URL for you, and instead of getting the usual properties window, I got a "FlashPlayer4" control panel.