I got the same thing playing as the Ottomans once I got to around the modern era. I was afraid it was going to **** up my hearing, because the volume was set pretty high, and that thing was ten times higher than what's comfortable. I mostly got it when looking around in enemy territory.
soundblaster live 5.1 latest drivers

very loud
Thanks Crunch for letting us know what the fix was, and thanks to Tattila the Hun for finding the problem. 