Hi Allan.
   Your idea to 'float' your instrument was a stroke of genius, since it decouples local
tilt noises.  I have posted your MKXXI paper at the top of my webpage
http://physics.mercer.edu/hpage/peters.html
  where I expect it to start attracting a lot of attention.  The Google guys love my
papers and I think they will find yours and post references to it on their search engine
in a prominent place.  Like yourself, I am satisfied that you ARE seeing the earth's
eigenmodes.  I've been observing them for many years, but the 'experts' refuse to
believe this is possible.  After all, since the best (most expensive) instruments in the
world can't see what is routinely visible in the instruments produced by 'rank
amateurs'; then we 'must be seeing noise'!
    The problem with the commercial instruments, as I have been trying to-no-avail to
point out to them for over a decade--is that their wonderful-for-earthquake instruments
do not function properly in the frequency range of the free oscillations.  In spite of
the remarkable excellence of some of the ones you mentioned (when it comes to technology
designed around conventional wisdom) these folks are 'wearing blinders' in several key
areas.  I view it as an 'inconvenient truth' for them.
   Let me explain what I think we both are observing, that the pro's refuse to
consider.  There are two obvious means for exciting eigenmodes, one type which they see,
and the other they refuse to consider.  These are: (i) the ones everybody recognize
following large earthquakes, and (ii) the ones I postulated years ago (published by my
student Kwon).  The latter I believe to be a class of oscillations that are unique and
generated by the following mechanism.
    The earth is like a multiply-cracked hard-boiled egg.  As it rotates under the tidal
forces, the 'shell' experiences 'snap, crackle, pops' that MUST excite the free
oscillations.  They are not long-lived like the ones following the great Andaman-Sumatra
earthquake, as an example.  Consequently, their linewidth is broader, according to the
uncertainty principle (Heisenberg's name appropriate to the understanding from a physics
perspective).  Incidently, I am glad to see you reference A. A. Michelson in the context
of the tiltmeter physics.  Don't know if you're aware of the fact that he won the Nobel
Prize in physics for the interferometer he designed (he was also a graduate of the Naval
Academy).  When I was a visiting professor at West Point I saw one of his lab
notebooks.  The calligraphy-like description of the experiments being performed told me
much about his careful attention to details!
    One thing for you to keep in mind--there is no noise source of traditional (random)
type capable of generating spectral "doublets", such as you show in one of your
plots--corresponding to the modes S07 & 0T13 / S04 & 0S12.  I saw other examples of the
same thing in your plots--which are very similar to ones that I have been observing for
about 15 years now.  I am delighted that you have come to the same place with an
ingenious instrument that should allow some correlation tests.  When I was at Texas Tech
University years ago, one of the geoscience professors there indicated what I knew (and
continue to hear from other pro's) is the following--if we can show that your instrument
and mine, separated by 2000+ miles, are oscillating at the same mHz frequencies; then
nobody who is rational stands positioned to dispute our claims.
     You mentioned your desire to extend your spectral plots below 1 mHz.  Larry
Cochrane has already done that for me, and I am sure he will give you the updated
WinQuake with which to do the same.  It requires, for plotting, that you export the
spectral data and then view it with Excel.  I will be happy to share particulars of the
method with you.  One of the other nice features of the Excel graphs is that you can
plot versus frequency rather than log-frequency (the eigenmode spectral lines show up
better this way).
   Thanks for sharing your results with me,
Randall