Thank you for all of your excellent suggestions. Luckily,
I found an inexpensive solution.
My receiver doesn't have a phono input, so I had a $75
phono -> line converter, which had a regular 110 plug. I
happened to have a $25 Radio Shack 9v battery powered
converter, which causes no noise whatsoever!
The proper solution, of course, will be to go and spend a
few thousand on amps & preamps and rewiring the whole house
electric system. Until then, I am able to enjoy hum-free
music.
BTW, is a "phono stage" the proper term for this thing? Is
there an Audiogon glossary page?
Thanks again,
Mark