I'll reply to you all at once to save some time!
The prop is Aluminium a McCauley B2D34C53
The electric fuel pump can be turned on and off with no change, could the engine driven mechanical pump create RF?
The Mags were removed, disassembled and overhauled, they check out fine.
The noise in only on recieve, only VHF and only the aircraft hears it.
Having the squelch off makes no difference. 2 Radio's fitted to the aircraft do the same thing. One radio was totally replaced with a new unit that did exactly the same thing.
I have tried taking a hand held on a flight and that never picks up the noise, so when pointing at a station the built in radio will get 2's and the hand held will get 5's I can have the antenna of the handheld quite close to the aircraft antenna and with the same line of sight. This seems to suggest it is something that is leaking into the aircraft fuselage from somewhere.
I have not tried no antenna yet, I will try today.
Thanks for the suggestions.