Hi, there could be a few possibilities that contribute to this problem:
1. You have not installed the correct AFPD patch. Try installing the latest patch 1.11.7.21 http://www.aerofly.com/www/downloads.html
2. It may be a problem with the graphic card driver. Update your driver and see if the problem goes away. You also need to ensure that your graphics card hardware acceleration is at maximum.
3. It could also be an overheating problem in the computer or card incompatibilities. Ensure your computer is properly vented.
4. The problem may also be the sound card driver. Update your driver and see if the problem goes away.
5. If you're using an on-board sound card, you may want to try disabling the directsound hardware acceleration.To change the audio hardware acceleration setting:
1) Click Start, and then click Run.
2) In the Open box, type dxdiag, and then click OK.
3) Click the Sound tab.
4) Under DirectX Features, move the Hardware Sound Acceleration Level slider all the way to the left (no acceleration).
5) Click Exit.