Older Pioneer Plasma hums through the speakers some, connected to Comcast digital cable via HDMI. Had the the Comcast guy out and he said the signal was too hot so he took their old stepup amp out of the circuit. No help on the hum.

One thing we noticed was that when he reconnected the coax to the back of the Cable box there was an audible hum as he made the connection-sort of a little like plugging a guitar into an amp with the amp on already. Cable guy said, "never heard that before."

I had somewhere to be or I would have had him keep at figuring out what that was all about but I couldn't.

Is there anyway that the "hookup hum" would be normal? Symptom of what then?

JB

Record a program on the cable box and then disconnect the cable connection from the cable box and then play the recording.
If there is no hum then the problem is that the cable connection to your house is not properly grounded and you hearing hum from what is called a "ground loop".

Just for grins I tried something else. My power brick has coax input on it-I suppose for surge. I put connected the Comcast coax to it, cabled to the TV-and the hum is gone. I guess my cable isn't grounded.

Should I complain to Comcast or just be glad it's not humming no more?

JB

It appears that the ground in the Power Brick/strip is the same as that of your Cable Box that is acted to ground your cable. It would make sense to complain to your cable company so you don't again have the problem.

Grould loops with cable TV are not unusual. I am always surprised when I hear that the guy from the cable company does not know what it is. It just means that there is a voltage difference between where the cable wire is grounded and ground at your TV set. If the problem is small enough that grounding the cable at the set via your power brick solves the problem I would say you are good to go. There are ground loop isolators on the market for cases where the problem is worse and grounding the cable near the set does not solve the problem. I use one from Jensen Transformers (VRD-1FF) that works very well. It seems that most cable guys have been trained to hook up cable boxes but know little or nothing about television or electronics in general.