TV sound bar 'hums' when TV is connected to cable

Whenever I connect the coax to the back of my TV (Visio HDTV) I get a hum from the (also Visio) sound bar. It doesn’t matter what source I use for video, it just hums when I connect the cable then it goes away if I disconnect it. Hum is a low pitched sound that can be drowned out with mid volume (but still present, just hidden by noise), and is very noticeable, at low to no volume. Any suggestions?

Look into “60hz hum” or “ground loops”.

My quick suggestion is going to be to make sure everything involved with your TV (so your TV, DVD player, cable box, etc) are electrically connected. The easy way to do that is to make sure they all use 3 prong plugs and are all connected to the same outlet/powerstrip. Assuming they don’t something else you can try, at least for now, is to connect them. Get some copper wire and get it to touch all the metal cases on everything make sure you include the TV, the soundbar, I’d specifically wrap it around the the coax. See what happens.
Alternately, (but along the same lines), take a look where your cable line comes in. If the Cable Co provides a way to ground it, do it there. Often times, you can run a copper wire from there to your breaker box’s ground wire. If this is a ground loop issue, that alone might solve it.

However, ground loop/60hz hum, IME, can be notoriously difficult to hunt down. At least yours seems to be related to the coax line, so that’s helpful.