It seems that you are having some issues with the audio signal that comes our from your Slingbox PRO HD.
The first step is to check if all the audio cables are properly connected. Since you have not provided further details, I recommend you to unplug both of the audio cables and verify if they are working fine. You can also use a second TV source in order to make this test.
You can also check the following link in order to apply the necessary troubleshooting steps.