GM Radio - Seems to fade in and out

I just bought this car used it is a one owner vehicle and has 212,000 miles on it. Seems pretty clean for the age and the owner seemed to take care and service it, so he says.

Owner said the radio does not always work, sound wise. Said he thinks there is a loose wire somewhere.

When I drove it home I ran through all of the radio options, settings. What I found is the radio works, but intermittently the sound goes away and it does not seem to be associated with bumps in the road either.

When the sound comes on it works as it should, but without notice the sound goes away.

Does not matter what mode you are in or any of the other settings. I cycled the mute switch on the steering wheel and it had no effect. When there was sound it muted and unmuted as it should.

Looking for general troubleshooting guidance.