Yes, try the amp in different outlets around the house. Certain appliances like refridgerators and air conditioners can cause sounds like this, even a TV. My TV used to cause hum in my amp, I would turn the TV off and the hum would immediately go away. Flourescent lights especially cause noise and hum on guitar amps. You may find simply using a different outlet will eliminate the noise.
There's all sorts of things that can cause noise in amps, one day I was practicing and heard the Police talking through my amp. I looked out the window just as a Police cruiser was passing by.
If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis