PA speaker hum at certain venues

[Al Krow]

Been getting hum through the PA speakers (RCF 932 and previously 912s) at certain venues. Assuming it's down to the electrical interference from the wiring. Is there anything that can be done to minimise?

[Bill Fitzmaurice]

Hum is almost always caused by grounding/earthing issues with the wiring and there's seldom anything you can do about it. 

[warwickhunt]

Worth looking at whether all the sockets are on the same ring and seeing if you can plug into one set of sockets; obviously being aware of the load placed on the socket.

[TimR]

Pubs? Check for a freezer or a light dimmer switch.