Popup blockers usually have a bloop or sound. But to rule out the blocker as a cause, check the settings. Turn off sounds.
My first instinct is that it's coming from your AOL. When you checked the sound settings, did you check Do not play any sounds under all the categories? If not, try checking that option, see if the bird call stops.
One of your buddys may have what AIM calls an expression that sounds like a bird whistling.
When that person signs on to or leaves AIM, you could hear that sound if you have Play the Expressions Buddy Sound of any user checked.
Edited by Queen-Evie, 26 April 2008 - 02:09 PM.