Well I'll give up soon, I'm starting to run out of options... (I have one more up my sleeve though!).
I ended up calling Jim's, and the guy who came out seemed to know his stuff, and had a lot of gear and was able to work out that (a) the antenna I have isn't strong enough for the area), and (
it wasn't mounted in the right spot. He wandered around the roof, and found he was able to increase the strength by 6db by moving it further along the house, and a bit higher up.
He also found the gain on the masthead amp was up waaaay too high.
I spent a couple of hundred dollars getting a "better" antenna installed (well he said it was better, a DC21A I think it is), on a much stronger mast as well... I saw the before & after results on his gear, and there was definitely a big improvement. He was very happy with the result. He also moved the power injector into the roof itself... which means it'll be easier later on to add extra coax around the house.
He did the work on a nice warm day, and basically - he fixed it. For the rest of the day I didn't get ANY glitching, and I even put the washing machine on ..... nothing! It was perfect!
Queue two days later... and BAM, it's back to how it was again. Lots of glitching with the washing machine on, and random glitching.
This is ridiculous... and it doesn't make any sense. How can it work perfect for a couple of days then return back to how it was?
Now that the injector's in the roof, I will buy 20M of decent quad shield coax, crimp on some F-connectors and run it along the floor from the TV (via the manhole) to the injector.... basically, keeping it right away from all power lines... that'll at least show if it's the current cabling in the wall that's causing the problem.
Other than that, I'm all out of ideas.
Edited by webbiegareth, 16 August 2010 - 03:14 PM.