No, that's the problem.
As I mentioned before I haven't changed anything. The only thing I could remember was the installation of the newest directx version. No mods, just the original installation of arma and the patches.
I 'll try to reinstall my sound driver of my X-Fi Platinum with the original openal drivers from creative. I hope this will help.
But thanks for your efforts!
If I found a solution I will tell the community!
Greetings from germany!