I made my own built in amp for my A1200 tower, at first I powered it using the main PSU but the this resulted in lots of strange noises coming through the amp. The simple cure was to place another small PSU in the tower from which to run the amp from...
It would seem that without adding extra filtering on the DC supply to any audio device that uses the main PSU results in all this crosstalk, anything from moving the mouse, windows being drawn or HD access all result in this 'interference' on most audio devices using the main PSU...
