Cheater plugs are for ground loop hums, which you hear through the speakers. Cheater plugs won't solve your problem if you have mechanical hum.
Your transformers are humming inside the gear correct (Mechanical hum)??
One term used to describe the cause of the hum is "DC Offset".
One potential pitfall of issolation transformers or regenerators, is while they will solve the system mechanical hum, it is possible they will hum themselves since they are getting the same bad power the gear was getting.