I have a CODA CSiB v3 integrated plugged directly to the wall, without any shorting plug installed, no buzz, hum or any kind of noise while bias “ON” at any selected input.
I think the last thing you can try is to turn off all circuit breaker except the one for your amp, unplug everything from that circuit. power up the amp and see if the buzz still exist, if yes then the amp need to send for repair, if no buzz then you can plug back all electrical device one by one and see if buzz exist. If no buzz then turn on all circuit breakers one by one until buzz exists again so you will know what caused the issue.
I think the last thing you can try is to turn off all circuit breaker except the one for your amp, unplug everything from that circuit. power up the amp and see if the buzz still exist, if yes then the amp need to send for repair, if no buzz then you can plug back all electrical device one by one and see if buzz exist. If no buzz then turn on all circuit breakers one by one until buzz exists again so you will know what caused the issue.