Dunnersfella: Before you get on the warpath with the companies, I'd get someone else to demo your STB on their TV (relative or friend) and see what happens to them.
If it's fine - you'll know where the problem lies firsthand.
You won't be taking advice of anyone with a vested interest - it'll be your own real world testing.
Then, you'll know exactly where you stand.
As an aside, what brand aerial do you have? Is it a UHF / VHF aerial? Or a straight UHF?
Thats a good idea. Although you would think it would be unlikely that both of the units I've had have been faulty
the aerial is a big straight UHF. not a combo