The Problem
While the radio is playing, it suddenly becomes very quiet or inaudible.

The Resolution
1. Right click on the speaker icon in your system tray (at the bottom right of your screen) and click "Playback Devices."
2. In the dialog that opens, go to the Communications tab.
3. Select the "Do nothing" radio button and apply the change.

The Explanation
By default, Windows automatically lowers the volume of other applications for what it considers an application to take priority. By setting this feature to "Do nothing," you are preventing Windows from controlling the volume of smartCARS when FSX or another application is opened.