Nearfield Monitors Mission Pro SM6A

[harstro]

Hi,

I am uncertain as to whether this is the correct group to seek advice
from, if so please forgive me. But can you help?

I have recently purchased a pair of Mission Pro SM6A active nearfield
monitors. However, without connecting them to anything except the
electrical mains ( i.e everything else is switched off and there are
no jacks going into them from anywhere ) I can hear both a hiss and a
hum.

I have tried them on every setting. The volume set to zero, but I can
still hear these noises. I live in the UK. Is this supposed to happen,
or should they be absolutely silent when they are switched on?

Any advice would be appreciated. Or please point me in the direction
of the right group to ask.

Many thanks,

Anna :)