Hissing from Speakers/Amp?

I am getting low level hissing from my amp at the speakers (you have to get close to hear it but it is there) when all other components are off (except the amp)?

Is this normal with mid to higher end amps or what might be the cause of it. Btw, I did sustain two dips and surges to the home's power supply and this happened afterwards but the amp was connected to a decent surge and spike protector and the fault light on the amp didn't come on.

Any thoughts would be appreciated.