Usually this kind of issue has something to do with the cabling. First, I would try making sure you didn't mix up the red audio cable and the red video cable (since there is more than one red cable when you're connecting the cable box to the Slingbox using component cables). Try switching them around on both the cable box and Slingbox (or Slingbox and TV if it is just your TV that is experiencing the issue).
Outside of that, I would make sure all your red/white audio cables are firmly plugged in, and if none of that works, try a different set of red/white audio cables.
Hope this helps!