HDMI cables run electrical signals through twisted pair wiring, and like any other sort of cable, can suffer from radio frequency interference. You can identify HDMI interference by seeing some speckles (usually green or red) on your high-definition TV. Sometimes the HDMI cables are the cause of the interference; at other times, they're picking up interference from another source. If you're experiencing the symptoms of HDMI interference, try the following steps.
Try your existing cable on a known good setup – use your HDMI cable as a test run between another computer and monitor, or between another DVD player and an HDTV. If the problem persists with your cable and does not persist with the other cable, the cable needs to be replaced.
Use a known good HDMI cable with your existing HDTV setup; your existing cables may be of low quality or have insufficient shielding. If the problem persists, one of the two devices you're hooking the cable up to produces a lot of RF interference.
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Use an RF-shielded HDMI cable – these can be identified by the ferrite nodules at either end of the cable, that look like fattened cylinders under the cable's protective covering. These ferrite nodules are there specifically to dampen or eliminate RF interference.
Avoid running HDMI cables for longer than 4 to 5 meters; the longer the cable run is, the likelier it is that the wiring itself will act as a low-grade antenna, picking up RF frequencies.