looking into the issue of hum on the Classic.
it seems that it is not uncommen, but there is a solution that many ignore.
in the manual on page 8 it says.....
If you notice hum in the system, remove the interconnects and replace them with very cheap, standard VCR interconnects. These are well shielded and should eliminate the hum. If the hum goes away, get quality, well shielded interconnects.
this makes sense, and you have had some success with rerouting your cables.
maybe trying a mat will also help, and it may help the sound.
it is trial and error of course.