Hi Hagen
Thanks for your post, I suspect something like that, but I have not the equipment or expertise to investigate as thorough as you have done. I will just keep looking for something that might be upsetting the IR through elimination.
I will also move the system to a different room or even building.
The only things that have changed in the house recently are :-
WiFi router, new microwave / dishwasher and oven, new downlighters in kitchen ceiling
I have tried it with the plasma tv switched off and the PC switched off
I will let you know if we get anywhere
Thanks for your help
Tony