Hovland HP100 hum?

I have a Hovland pre and VTL ST150 amp. Connected to the Alto Utopia Be speakers through synergistic research cables all around. The hum from the Hovland is too much. I can hear it from my listening position. I am using cheater power plugs, so I dont think it is the earth connection.

Any advice or ideas? I think I read about the Hovland hum in some of the reviews.

Thanks.--Michael