  Even in absence of earthquakes, each site on earth experiences continuous
elastic vibrations which are mostly traced to the non-linear interactions of
sea waves. However, the fine structure of the spectrum at mHz frequencies shows
hundreds of highly significant narrow bandwidth peaks, with a persistence and a
coincidence with solar acoustic eigenmodes which are incompatible with any
geophysical origin. The feasibility of a common cosmic origin is evaluated
through an estimate of the gravitational wave cross-section of the earth,
combined with its elastic response and with the stochastic amplification
produced by the interference of the cosmic signal with tremor of oceanic
origin. The measured spectral peaks appear compatible with a gravitational
monochromatic illumination at strains $h \gtrsim 10^{-20} $. We analize in
detail the band around 2.614 mHz, where the binary white dwarf J0651+2844 -
which is the second strongest known gravitational stellar source - is expected
to emit. Compatible spectral tremor peaks are found for both the earth and the
sun, but their amplitude is 3 o.m. larger than independent estimates, so that a
gravitational source attribution would call for a variety of unknown
non-luminous sources with definite mass-distance ratios.
