It may not be your MF power amp, (although it might be, as higher powered amps can have a bit of low level noise).
I suspect it is the Belles preamp, as it is a vacuum tube preamp. I believe you are hearing what is referred to as "tube rushing". It is normal, and should not be audible during all but the very quietest passages, like blank areas between songs.
Most people get used to it fairly quickly. Give it a chance to fade into the background, before you get too frustrated.
(FWIW, Unfortunately for me, this frustation from the tube rushing noise never went away. I eventually went all solid state to eliminate it. And to get solid state equipment that sounds as good as tubes, means spending a fair amount of money unfortunately!)
Good Luck and hang in there!
I suspect it is the Belles preamp, as it is a vacuum tube preamp. I believe you are hearing what is referred to as "tube rushing". It is normal, and should not be audible during all but the very quietest passages, like blank areas between songs.
Most people get used to it fairly quickly. Give it a chance to fade into the background, before you get too frustrated.
(FWIW, Unfortunately for me, this frustation from the tube rushing noise never went away. I eventually went all solid state to eliminate it. And to get solid state equipment that sounds as good as tubes, means spending a fair amount of money unfortunately!)
Good Luck and hang in there!