Update: I dont' like the first box that touches outside wiring to come directly to ANY internal device but more for fear of surges taking out everything connected to it than noise/audio issues.
In my case I have the cable company's router/switch comes in and it is air-gapped by fiber to my personal router.
If your service is via coax:
- Put in a gas discharge surge protector outside
- If it only connects to other devices via Ethernet, you wont’ have a ground loop issue, but if it goes to a set-top box that goes to HDMI or something like that you might. You’ll want a ground loop isolator.
- Consider for additional safety, or if you don’t want to use a coax surge protector an Ethernet isolator like this one: