Well, put up a new inverted-L antenna - 30 feet up a tree, 60 feet
across horz and over the house rooftop (nowhere else to go!), base ~20
feet from house. Using a winradio 9:1 unun matcher at the base, *not
yet grounded*. In fact, so far none of the RF chain on this antenna
is grounded. So far, so good - noise level *fairly* low (lower on
almots all freqs than my DX-Ultra), AND signal strength on most bands
roughly the same, varying depending on the band. One good thing I do
notice is that on strong MW stations, he antenna does *NOT* reveal a
60 Hz background hum like the DX-Ultra does - I consider this a good
sign. The far end is about 25 feet from the higher-tension power
lines out back, and the near end is about 15 feet from the low-tension
lines in front. Next steps -

1 - Ground the 9:1 unun
2 - Bury the coax from house to base of antenna (about 18 feet
underground)
3 - Install RF isolator (Either Radioworks or Wellbrook AFI5030) at
the house with or without a ground stake connection, depending on what
works the best.

Have not had great reception so far this week, so no chance to really
give it a workout.

Further reports to come. Thanks, guys, for all the input so far!