he's convinced it's an electrical fault (probably a grounding issue he said) and that I needed to get an electrician in to take a look and he'll come in after that if needed, possibly to ground the splitter he said if the electrician couldn't fix it.
It's the first thing I do if I strike a funny, but don't think it will fix your problem.
I read back on your posts and saw you are in a new house, so I didn't think bad connections or corroded switch contacts would be a problem., apart from the washing machine.
As I see it, (based on empirical testing I have done), house wiring can act as a loop antenna which conducts/radiates interference from arcing switch contacts (and other sources, washing machines etc). If this interference field impinges on the antenna, and the incoming wanted signal level is overcome by the interference, picture breakup occurs.
A tiled roof, such as you have, may allow more of this interference to escape and affect the incoming wanted signal compared to, say, a colorbond roof.
In any case, the solution, (if there is one), involves getting a signal at the antenna that is less affected by the interference, if this is possible.
This would usually involve the attending technician using a selection of antennas at different heights & locations on your property to effect the best countermeasure.
It also requires the use of instrumentation that can give a similar indication to your Sony's UEC, to assist with finding the best antenna location. A couple of hand-held transceivers are also useful, so you don't have to yell commands at each other when testing.
Even so, it may only be possible to reduce the problem, and not eliminate it entirely.
As an aside, I listen to 774 ABC Melbourne a lot. A couple of weeks ago, the morning announcer was talking about his woes with a new PVR that had been installed, and was having IIRC, glitching issues. Apart from laughing at the suggestions sent in by listeners, it struck me that people served by VHF digital transmissions have a lot of trouble such as you are experiencing, whether due to poor installation or poor signal issues.
I'm so glad all transmissions here that I get to work with are on UHF.