It's got to be something else. Of the dozens of amps I've had, only one had noise audible more than 3-4 feet from the speakers.
Quietest amplifier you have ever owned.
I hate it when I'm sitting in the listening chair with no music playing and you can hear the sound of the amplifier coming through the speakers. I was curious what the quietest amps out there might be. One example I can think of would be the Antique Sound Labs MG-SI15DT integrated amplilfier. With the amp on and no music playing I can put my ear right up to the speaker and hear nothing but dead silence. This is probably the quietest amp I have ever had and it probably has something to do with it's single-ended design.