Hi and welcome to Just Answer. I'm Steve, I'm sorry to hear about your issue. I will try my best to give you a precise and accurate answer.
We need to eliminate either the TV or the box/wiring as the cause of the problem.
So, do you have another box anywhere in the house?
Ha! Don't worry about that.
Can you tell me the make and model of the cable box please?
Ok, that's a Cisco box. I have one of those.
How often does this audio drop out occur? And you say it goes out for 2-3 minutes?
It could be the box. It doesn't sound like it is the TV.
Do you have a DVD player hooked up to the TV? Or something else like maybe an XBOX or Playstation?
If so, see if the sound cuts out while you are watching a DVD or playing a game.
Play a DVD and tell me if the sound cuts out.
Comcast recycles their boxes. When someone has a bad one, it is replaced, cleaned up, 'fixed' and sent back into the field. There is a very good chance that you have an iffy box.
Try the DVD. If the audio is fine then the first thing to do would be to change out the box.
Just ask if you need more help on this issue. I will be here.
Thanks very much.
1. Electronics go bad. And, as I said previously, your 'new' box probably isn't.
2. If the DVD has intermittent sound blackouts, it is not Comcast. That is your TV at fault.
If you have to get the box exchanged, you can have a tech come to your home, or you can exchange it yourself at your local Comcast office.