Hi,
Why the 47R in series with the PA power supply?
I assume all those DC-DC converters have the gnd inputs connected to gnd output.
Have you got the DC-DC connected to the 12V supply in star configuration?
Do you have a terminal strip for the 12V connections?
What supply noise do you hear, hum or hash?
If mains hum, you probably have a ground loop.
Don't forget the metal tab on the LM7805 is connected to gnd pin.
Tom... 
