small white bar showing on HD network channels

[aramis109]

The white bar/line is just overscan. Sometimes they put the subtitle information there (you can see black and white blocks alternating). Your only choices are deal with it or change to a different picture mode on your set that zooms in slightly. Your set is just displaying the picture they're broadcasting.

Unless your audio cuts out while watching other HD content (such as BD's) it's not a setting or your system, it's the bandwidth and compression. I would call your cable provider and complain.