Hum in ARC Ref 3 not on 0 but 1-103 light buzz

A "light buzz" could be a light ground loop. Try a cheater plug on the amp and see if it goes away. BUT, I don't think that is the problem.

A "sea whispering' noise is classically the 'noise floor' of the pre-amp or a couple of critical tubes which are, or have gone noisy.

I suspect the 0 position is actually a mute position and kills any output to the amp. In the 1+ positions any noise will be communicated to the amp and it will not vary with rotation of the VC, unless the noisce is accociated with a source selected, such as a phono source (especially) and then the noice will increase with VC rotation.
If you have a high sensitivity amp/very efficient speakers your noise could be noise floor of the amp. It could also be noise from the phono stage (if that is were your selector switch is set, especially with a low output MC cartridge.

Most brobably it is simple noisy tubes in critical positions in the line stage, or more likely the phono stage. Get some extras (soon or later you will need them anyway) and exchange them with the extant tubes and see if it goes away.

FWIW, my suggestions all have their origin in my use of an SP10 over the past 20 years.........:-).

Sounds like a ground loop hum. Since it wasn't there when you first bought the Ref 3, I can only assume that you have recently made some electrical change in your home that is now inducing this hum. It could be anything from new audio equipment, to new cable or satellite tv, to a dimmer switch just installed. So you have to start troubleshooting, thinking of any recent changes may be helpful.

This link may be of some help. Good luck.

Cheers,
John

Mine is dead quiet - no different than a SS preamp in fact.