Coaxial Cable Interferes with RCA Signal

For the CR4'ers: Just an EWAG here, but it may well be that he is using a cable specifically made for the purpose, that would be similar to these S-to-RCA adapters.

The S-Video circuitry in your video card separates the Luminance (pin #3) from the Chrominance (pin #4) and provides each signal separately. The other two standard pins (#1 & #2) are ground references for the others, and may be joined directly and soldered to the RCA outer bonding shell. If your card has additional pins, they are only for specific uses by that manufacturer, and should not affect use of the standard ones for video only.

The Lumi has a wide range from low to mid frequencies compatible directly with the composite input of your TV, but the Chrominance includes much higher frequency information that must be - equalized (for lack of better specific term) - before joining them together. Various references indicate preference for different "types" of capacitors depending on the form factor of the adapter, or additional circuitry if the signal is going to be reversible, but basically it's nothing more than a 470pF cap in the Chroma #4 lead, prior to #3 & #4 being joined to the center post of the RCA.

Now, knowing this, you still may have a need to ensure everything is properly grounded/bonded, as it "may" be that something came loose in your move to this new location.

But my guess is an impedance mismatch or straight out interference on your new Cable service coax.

Composite Video signals, whether transmitted through a poor old RCA cable or a nice RG-49 Coax, all want to transmit their way "into" the TV at the same 75 Ohm impedance as the TV circuitry, otherwise things get ugly quickly. *That's one of the biggest motivators for moving to digital.

RCA plugs and format are the worst because they not only use tiny stranded conductors that break more easily, but the plug connectors and the format itself is not capable of correctly "matching" 75-Ohm impedance. It was invented simply as a secure way to get an analog audio signal from a gramaphone over to a coupled horn. And here we're trying to use that connector to display Halo from a PC. Go figure.

A loose shield or connection in your new location behind the wall with your cable, interference on the shielding of your cable company incoming service, high voltage inductance or other AC voltage getting to your power supply ground, poor extension coax cabling, or damage to your S-Video-to-RCA adapter cable, could all cause some leakage of signal or a change in impedance.

Recommendations
#1) Eliminate any "extension" multiple cabling on your coax, by simply getting a cable that is long enough in the first place.

#2) Also, there should never be a cable company cable that just pokes-through-the-wall to screw directly into the TV. Make them do it right, by terminating the cable inside a back-box with a coverplate that gives you a wall jack. Gold-plated or not, that's the correct installation method to reduce other issues.

#3) If you have a separate adapter at the end of your S-Video cable, try replacing that cable to ensure no damage there is contributing.

#4) Have the service tech for your new cable company to do a ground check, to ensure the outside cable demark has the shield correctly bonded directly to your power utility grounding rod conductor, and do a noise/interference check on your coax. You don't even need to go into the computer video-card used on the RCA input issue, just tell them you get some interference and want it checked out.

They may be able to check your receptacle ground and neutral lines for noise as well, but you can use a multimeter to make sure there is no AC voltage between the ground plug and the neutral. If so, get the landlord to have his electrician out immediately. I say neutral-noise, because a loose neutral connection or improperly bonded or 'shared' neutral causes some strange behavior with electronics, and your TV likely has no ground, just a bladed plug for line and neutral. The computer, on the other hand, is 3-prong grounded as well, which is then the 'reference' for any signals paired with bonded 'ground' lines or shields, so that side should be good.

If you ever decide you want to purchase good cables, I don't want to make this sound like a referral as I have no relationship whatsoever with this company, but I have never had a problem with the engineered materials, construction, quality or value from this supplier: Blue Jean Cables

Though I despise Wikipedia's bias and censorship in many areas, technical articles tend to go unnoticed by the activists, so you may wish to familiarize yourself with the various portions of video signal issues:

Here S-Video
Here RCA Connectors
Here COAX F-Connector
Here Coax Cable
and Here Interference