External View Sound Problem

Recently, I noticed that there was no sound when viewing my RealAir Turbo Duke from the outside. Well, almost no sound - it's there, but at a very low level. Interior sounds are normal, I can hear RC4 traffic, everything else works normally. I checked some of my other aircraft and found the same problem with the default Lear and default Kingair. All of my prop aircraft and other jets seem to be ok. Adjusting sound levels in FSX makes interior levels go up or down, but not much difference in the external view. I haven't changed anything in my sound files and all my recent add-ons are prop aircraft. I'm using an audigy sound card with the latest driver. Dxdiag shows no sound problems.Any ideas of what to look for?Dale