Problems with sound on HDTV

[Maximillion]

Hi guys, I have a HDTV with 5.1 sorround sound and just yesterday this starts when I watch HDTV channels the sound is very low, even when I set the volume to maximum. On regular TV channels, the sound seems normal coming through the speakers. When I do a speaker test through my DVD everything sounds fine. Could this be just some problem with Comcast (my HDTV provider) or some type of hardware problem?