I have my audio going to my Pioneer receiver so I don't need the audio going on to the Elite 1140 plasma.

I thought I remember some where you could turn off the audio portion and I can't remember if it was on the Comcast HD DVR 3416 or the plasma.

Why? Aren't there times when you may want to listen to the TV without the A/V system? There's no harm to leaving it as it is... unless you have a problem (which there's no reason you should).

If you must.... since you already have the HDMI directly to the A/V receiver, just disconnect all other audio cables running to the TV.

If you have HDMI running from the A/V recieiver to the TV, you can turn the volume completely down on the TV if not needed.

Well I didn't hook up the speakers on the plasma so I don't have to worry about volume on the TV.

I must have misunderstood you, I don't have an HDMI capable receiver so the cable box goes directly to the plasma and since I don't use the plasma's speakers I have a coax audio cable running to the receiver for audio.

The reason I ask is that when I was just listening to the music channels on the cable box I noticed that audio started coming thru the speakers and then it went away for a second and then comes back. I don't know if this has something to to do with going from a HD broadcast to a SD.

It shouldn't have anything to do with any audio switching from SD to HD... that's video.

The only thing that may be an issue is the setup or the make/model of the STB where it's not handling PCM stereo (music channels and non-DD programs) properly. Or perhaps... poor signal from the cable provider.

The reason I ask is that when I was just listening to the music channels on the cable box I noticed that audio started coming thru the speakers and then it went away for a second and then comes back. I don't know if this has something to to do with going from a HD broadcast to a SD.
It could just be glitch in the signal.

It could also be related to HD to SD. Many HD stations are DD5.1 which the STB passes through. SD stations sometimes get sent out as PCM by the STB. You receiver might have a slight pause as you go from one to the other.