...IME this is more common when listening via the built-in HDTV speakers, which generally do not provide the best quality sound- even on so called 'good' brands per se.
Try adjusting the sound parameters on the Phillips HDTV menu to see if that does anything (e.g. stereo/matrixed stereo/etc.). Also look in the Comcast box settings too. There may be at least one or two small things you can change there (it has been awhile for me, so I don't recall what's there on their Moto boxes at least).
We have a 32" Philips (Phillips) HDTV (720) and the picture is great. But the audio is really a problem. We use an HDMI cable from our HD DVR/cabel box from Comcast.
In nearly all programming, the ambient sound and soundtrack music overpower what's being spoken by the actors. It is really bad with sports programming in which the crowd noise totally drowns on the play-by-play/color commentary audio. In fact, I can hear the QB on the field call out audibles lounder than the announcers.
I have tried the audio options for the TV but it doesn't solve the problem. What else can I do? The Philips help desk just read from thei manual and have no expertise.