SYMPTOMS: (audio hums, but does not know the words)

A. There is a low frequency hum coming from the speakers or subwoofer.
B. There is a Faint Horizontal line, drifting up or down in the TV picture.

Indicates there is a ground loop, which is relatively simple and inexpensive to fix. A ground loop occurs when two earths or grounds (not one) are connected to your theater system, audio system, multimedia computer, TV, etc…
This also frequently occurs in professional PA systems, musical instrument amplifiers, and recording studios.

Most common cause: cable television. Disconnect the cable TV entirely (this includes cable internet) and test to see if the hum goes away.
If the hum goes away, you can install a cable TV isolation transformer, available from several electronics supply houses. OR use a cheaper method:

Easiest / cheapest solution: A three prong to two prong AC power plug adapter, sold in hardware stores. This is intended to adapt a new style AC plug (with ground) to an old style electrical outlet (two prong). The new style AC power plug has a third pin, which is a ground.

The adapter allows you to “lift” the third pin, which disconnects the ground from the TV, amplifier, etc…Please do not cut the third pin off the power plug.
The adapter may have a green wire or a grounding tab, don’t connect those to anything…

Once the offending ground has been disconnected, the ground loop will be gone.
Install the plug adapter on the TV or subwoofer first, you may need more than one adapter. Did that solve the problem?
If not solved, try lifting the rest of the grounds in the system, such as PC, Mixer, etc…you will certainly find the source of the ground loop by process of elimination.

Hope that helps your hum and TV picture. :bounce:



Oct 15, 2007
extra ground lingering on the circuit board can cause problems.
the circuit might behave differently (which could be a bad thing or a good thing)

the extra ground would also cause the pieces on the circuit board to age faster than they normally would.

i can hookup my receiver to the soundcard.
the cable box to the soundcard.
cable box to the television.
all of these without seeing or hearing a problem.
but when i connect the graphics card to the television, i get the 'hum bar'

what is funny about it though, none of my pieces of hardware have a ground plug except the computer.
but as soon as i disconnect the coax cable from the cable box, the hum bar goes away.

so if what soundguruman said was completely true, i shouldnt be seeing the hum bar.
i went outside and checked the splitter.
its grounded to a metal pole.
i dont remember, but i think the pole is a utility pole that accepts the electricity wire from the pole.
maybe i could get a ground spike and put it in the ground.. then ground the splitter to that so i know for a fact that the splitter is grounded.
but that still doesnt say much about removing ground plugs until only one remains, because my setup only has one ground plug.

i hate being in this situation.. all of my details are perfect for consideration except one thing.
i dont know if that pole is grounded.
but it looks like the ground strap is professional.
and i dont know why the cable installer would send a ground wire to a ground strap on a piece of metal that isnt going to fix the ground problems.
because the machine that they bring into the house to check signal levels should inform the installer if the ground strap is working or not.. right?


Mar 26, 2010
If you have an ungrounded cable line coming into the dwelling, I do not recommend defeating the ground portion of the plug. The current makes a neat path through the mainboard of the television, and leaving it in place will damage connected components and the tv.

Bad AV cables can cause the hum you describe, and an easy test is to simply wiggle the ends - if the hum changes, replace 'em.

To make a long story short, it is against code to have voltage over cable lines past the point-of-entry to the dwelling. If you have this situation, unhook the cable from the tv and call for service. If you are brave, go outside and find the ground wire that come unhooked from the splitter and reattach it to the house's ground stake.
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