I returned the RS speakers and purchased a pair of Genius SP-HF800A 'headphone jack' speakers from Amazon for $49.
The hum is completely gone.
I noticed base distortion on a sports channel that broadcasted an athlete with a low male voice--I think I mitigated the problem turning down the base on the speaker. I now have the tone set to the middle and will listen for a few weeks before making the final decision whether to keep the speakers. Otherwise, the sound (for cheap TV speakers) is really good.
So the initial Logitech speakers with the awful hum were 5 watts, the RS speakers were 16 watts and the Genius are 20 watts.
One could then make the argument that getting rid of the hum has less to do with 'better' speakers and more to do with more powerful speakers--unless better speakers are naturally more powerful?