Entrance Coax Cable causes hum in Home Theater system audio

When I disconnect the entrance coax cable from the outside ground block the objectional 60Hz hum in my theater system speakers is gone.

Hence, there is no internal ground loop within my home with all the system components connected.

Also, with the entrance coax cable connected at the outside ground block and I disconnect the Coax Cable from the STB (XG1v4) or disconnect the STB HDMI cable from my home theater system the objectional 60Hz hum in my theater system speakers is gone.

I have a #6 grounding wire to an 8' ground rod within 4 ft of the entrance coax cable grounding block and the balance of the home is properly grounded.

As I have performed the appropriate troubleshooting procedures there is no internal electrical ground loop within my home causing the objectional 60Hz hum and only with the entrance coax cable connected at the outside ground block is the objectionable 60Hz hum present.

Finding: With the entrance coax cable disconnect at the outside ground block, I measured 200-300 mv ac between the ungrounded entrance coax cable shielding and the coax cable grounding block.

What is the standard for the acceptable AC Voltage on the entrance coax cable at my home?

Is this entrance coax cable grounded at the Xfinity distribution point coming to my house?

How can this ground be tested?