I have a hum on all inputs which my dealer informs me is due to an earth problem. Unplugging the interconnect between the 555CD and 552 resolves the problem but means I can't play music obviously . To be fair, my dealer has tried really hard to fix it but without joy. So far we have tried the following:
Different interconnects (several!)
Running a long extension cable from different electrical sockets.
An electrician with HiFi experience checking the supply.
Substituting the CD player (including PS).
Substituting the preamp (including PS).
Yet another interconnect, this time with earthing crocodile clips at the source end.
Really frustrating. My dealer is going to escalate as high as possible at Naim but thought I'd raise in case anybody has helpful thoughts.