Just bought a SV212H with matching SV212 cab.

Even when the high treble volume is just above    Zero, there is a very noticeable hiss that is almost as loud as the guitar sound when playing clean.     When playing at home volumes and you let a chord ring, you can hear the hiss, surely this can’t be normal? The more you turn it up, the louder the hiss gets.

The normal channel 2 doesn’t have this hiss at all, even when really turned up. 

Is there a fault with the amp, or is this normal? 

It just really spoils playing moderate/low  volumes with  clean sound, I’ve never known a Marshall do this before. 

The official demo’s of the amp by Marshall don’t have the hiss when they pause playing or let a note decay. 

Help!