Wayne,
I believe Foster is right on the money; this is usually a mains contamination problem.
Now, on the GK-1 you can use a filter since it's all Class A circuitry. But on the AKSA 100, things are different, since the mains current varies with signal and any impedance between power source and amp will generally be audible. Accordingly, use some caution with these gadgets, and if possible try before you buy as some will degrade the AKSA sonics.
Back to NZ, huh? Are you looking forward to this move? A better job, perhaps Wayne?
Cheers,
Hugh