Fsx Sound Problem

The sound in Fsx cuts off or mute at 5 min. interval. It starts again with a mouse click anywhere on the screen. This has no effect on the simulation itself and the entire flight could be made without sound. This problem does not affect the on/off sound from key Q, nor is it affected by the sound settings in Fsx. This problem is only present when Fsx is running as it never occurred on any other program on my system including music from CDs. I checked the sound settings in Fsx.cfg and these appear normal. The problem started when I installed a local network involving a second computer. The problem occurs even when this second computer is inactive. It would be nice if I could extend the 5 min or suppress this cutting of the sound. I would appreciate any comments or suggestions to solve this problem without having to reinstall Fsx and all the associated files. MauriceSystem: Windows XP SP3, Fsx SP1, nVidia 7900, 4 Gb memory