Xpantastic!

Hi. I've an Xpander that works good, but there is some humming noise from the PSU. A little research on the net revealed that this is quite common to the Xpanders. Is there anything I can do to remove the humming, or at least make it hum more quietly? Can I replace the power transformer? If so, does anyone know where a new one can be obtained? I've the USA version. Many thanks, Mattias.