I have a Toshiba CX32D70 that when I turn it on, sounds fine. But after several minutes the sound fades so that it's only audible if I turn up the volume as high as it goes. When we use the XBox or any other device coming in on video 3, everything is normal. The picture is unaffected no matter what, so the set seems worth keeping. What could this be and how can I fix it? Thanks!