I"d replase it pronto, and if the next one does the
same thing, there's something "differnt" somewhere. A
GFCI, AFAIK, only hums when it's defective or under
heavy load. The TEST button is an indicator of whether it's working or not, but it's NOT necessarily an indicator that it's tripping WHEN it should, or of how much protection it's affording. Stuff happens, so check it out. Is this new? How long has it been doing that? Etc.
While you're at it, check out the rest of the things on that line; is there a heavy load there and is the switch rated to handle it? Is everything else working correctly?
Cheers,
"CL (dnoyeB) Gilbert" wrote: