I have a Hicap (non-DR) purchased in 2013. It has always hummed and been a source of annoyance. Humming power supplies comes up on the forum frequently. The general conclusion seemed to be Naim power supplies hum and this is normal and to do with problems with the mains supply, the power supply itself was not at fault.
Recently I brought a s/h Supercap fully expecting it also to hum but the Supercap is totally silent.
Is there evidence that the Supercap is just better able to reject whatever mains pollution causes the hum?