Most likely explanation for the noise you are hearing is DC offset hum. The root cause is the US is a 240V country with transformers designed to provide half the voltage to two "legs" of 120V each. This is why panels are always two rows of breakers. One side is one 120V leg, the other side another 120V leg. This is why 240V breakers take up two slots- they get 240V by physically connecting to both legs.
Problem is the 120V of each leg is reference to utility neutral. Both 120V legs return to the same single neutral. Normally, fine. Every once in a while though the draw on one leg can result in a voltage differential, aka DC offset. In practical terms your dishwasher and blow drier draw enough current to cause DC offset and your noisy transformer.
You don't say, but that's almost certainly what it is. The first thing power does in any amp is go through a power supply transformer. DC offset typically causes transformers to vibrate and produce an audible hum. Listen real close to the amp, if it is coming from the transformer then DC offset for sure.
Not a big deal, really. Unless it bothers you, in which case you get a Hum Buster or other device designed specifically to address DC offset hum.