Hiss in audio when people speak - XFinity

We have the digital starter package. One one tv we are connected via CISCOUDTA - adaptor. About a month ago we began to notice that there is a lot of hiss noise whenever someone on the screen says anything with the letter "S" in it. News, regular programs, all channels have this issue. Sounds like snakes hissing.

I've checked to make sure all cable connections are tight. There's nothing new to cause interferance. I've adjusted the audio settings on led tv. Still cannot get rid of the hiss.

The other tv is connected with a basic settop box and has no issues. Other than On Demand blinks out.

Do we need a service call?

Thank you,

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