How to get rid of transformer hum?

I realize that you have measured a 5% sine dip. But are you certian that this is the cause of the hum? I have tracked down a lot of hum problems and most are generated from within the home. I will relate my own personal experience. I always had a slight hum in my tv and Tice isolation transformer for my gear. I lived with it until I bought a Classe CA400. The amp hummed very loud! I finally isolated the source to my heat pumps outdoor unit. Something in the prehaet circuit of the compressor. Right now I just turn it off when I listen. The background is dead silent! I'm going to look into it deeper when I get the unit pm done. I would try turning things off in the house first to see if the hum is caused internally. (off means off at the breaker) Good luck!

Tommy, have you tried to power these amps at another local? Away from your home? I saw that the mfg stated that its a power problem. I may not be an EE, but I have over 20 years in the field and 9 times out of 10 its not the equipment or the power but another source of noise on the line saturating the transformer causing it to hum. I know we all hate the power company and sometimes they are at fault. I'm just curious as to whether the problem follows the amps when they are powered somewhere else.