noise and background loops in SID?

[bosone]

i was looking thorsten schematic regarding the C64 power supply for the SID.

he speaks about ground loops and of some tricks to lower the noise at 50/60 Hz.

where can i found some info rgarding this topic?

i plan to build my own power supply unit, because i will also need +15/-15V for an analog filter.

since in the C64 case (see my other topic!) which will i use there is not enough space to insert the power supply module, i will make an external one, using a cable to drive the +15,-15,+12 (or +9),+5V alltogether. every voltage will have his ground wire.

is there some drawback on this configuration?

(i will mount caps on SID and core module, the ones after the 7805/12 regulators)

another though: the C64 case i will use is made of plastic, not metal: will this bring problem with regards to the eletric insulation against interferences and/or noise in audio signal??