Hum in a Kora Eclipse phono section

A friend has a kora clipse that has developed an odd "hum" that is either in the phono section itself or that the phono section is amplifying (he can hear the hum when the phono input selected and the turntable isn't even connected to the preamp). Swapped all of the tubes and still no luck. Any ideas? Just wondering if it might be something simple, or at least if we can do some diagnostics before sending it out. Where can you get this serviced in the US? Near NYC, NY or can ship as necessary. Any help would be appreciated.

Best regards,
Alan