While it isn't clear from discussion so far, if there is raw AC being rectified, you must pay attention to reservoir cap charging currents.
I prefer to think of every wire or circuit board trace as a resistor, to visualize and deal with voltage build up on traces.
The current path between transformer winding, to diode, to capacitor, and from capacitor, back to transformer should be a clean simple path. The node between the ground leads of the two reservoirs should be low impedance (short) and from this node, a single path to regulator ground references. The current flowing in the ground reference path will be DC or audio so not a source of hum.
There will be peak currents many times higher than average current in the cap charging loop, so keep these paths isolated so they don't contaminate clean grounds. Also in extreme cases look out for lead dress of transformer leads as they will carry high peak (hum) currents. It's all pretty simple once you visualize what is going on.
JR
