Common mode signals.

What is it?
When coaxial cable is used for TV, radio, or CB, the signals on the inner and outer cables should be equal but opposite. In this situation, the fields created by the two signals cancel out - giving no radiation.
In some situations, both conductors are carrying the same signal - which is then referenced to earth.

What can suffer from interference from these signals?
Any kind of electronic equipment.
As the signal may travel through various paths to return to the common point (earth), it can go through different circuits, could be re-radiated, and can cause different symptoms.
It has been known for a video to suffer with interference only when playing back videos - you could watch TV through it as normal.

Tip. Interference to other equipment is the usual reason for a visit from enforcement agencies. Even if you are not to blame for interference, you would get busted for any illegal equipment found.

Who's fault is it?
This is usually avoided with good design, so it could be down to design of the equipment suffering.

What causes it?
This can be caused by signals being picked up on the cable, rather than coming from the device at the other end, such as the antenna.

What should I do about it?
This can be treated mainly as you would for overload.

Antenna position:
Wherever possible, your antenna should be mounted as high as possible, above television and radio antennas. Also, it must be remembered that TV antennas are directional - placing your CB antenna behind a TV antenna, rather than in front, may help to reduce the amount of signal getting to the TV.

Coax.
The use of old or cheap coax may cause more signal to be radiated by the coax, rather than the antenna. This signal may be picked up by your neighbours TV or radio, rather than other CBers. The position of your coax can also be important. It should not be placed next to TV or radio coax.

Antenna tuning:
Poor tuning of the antenna can cause the coax to radiate signal, which will be lower to the ground and closer to other equipment. It is in your favour to make sure that as much of your signal as possible is sent out at the antenna.

Do not leave your SWR meter in line:
As the SWR meter can cause losses and produce harmonics, it should only be connected while testing the antenna.

High Pass Filter:
If all else fails, a filter in the TV coax can cure the problem. The best type of filter to use, is the Braid Breaker type. These cost more than the basic filter, but are more effective.
This filter should be plugged directly into the socket on the back of the TV, not further down the coax. If the person has a video, the filter should go into the back of that, and the lead to the TV should be short as possible.