Secondary display (TV) making main display blink

I have a dual monitor setup on a Mac Mini - the main display is connected via a Thunderbolt to DVI adapter.
The secondary display is the TV connected directly to the HDMI out.

I've recently upgraded the TV and am facing a strange issue. Everytime the TV is using another HDMI input (cable or Playstation) the mac's main display blinks, a solid black screen similar to what occurs when one changes a monitor's resolution. Two black screens in quick succession, then all's well for around 15 seconds and the cycle repeats.

By clicking the display icon in the menu bar I noticed that the Sony TV listing disappears immediately after the first blink and reappears after the second blink (a second or so later). So basically, the Mini ceases to see the TV every 15 seconds and then immediately detects it again.

I tried playing with the power settings on the TV, and on the Mac side I tried turning mirroring off. I even disabled the Sony TV on the Mac using a third party utility to no avail. The only thing that works is unplugging the HDMI cable from the Mac.

If all else fails I'll get an HDMI switch so I can use it to disable the TV's HDMI when not in use but it would be dirty solution. I didn't have any such issue on my earlier Bravia (a 32" model, the current TV is 40"). Any ideas would be most welcome.

Edit: I currently have a 10 meter HDMI cable, would replacing it with a 5 meter high speed cable help?

 

I haven't tried it with another HDMI cable because I don't have one that's sufficiently long. I plan to get a high speed cable that's half the length of my current cable if I can't solve this a better way. My current cable worked fine with the previous TV though, and it mirrors perfectly too so I doubt it's faulty. It could be a problem still if it's too long for the new TV's signal strength.