  In this Letter we further explore the idea, suggested previously by
Klu{\'z}niak and collaborators, that the high frequency QPOs may be explained
as a resonant coupling between the neutron star spin and two epicyclic modes of
accretion disk oscillations. We confirm result of Lee, Abramowicz and
Klu{\'z}niak (\cite{Lee2004}) that the strongest response occurs when the
frequency difference of the two modes equals either the spin frequency (for
``slow rotators'') or half of it (for ``fast rotators''). New points discussed
in this Letter are: (1) We suggest that the coupling is gravitational, and due
to a non-axially symmetric structure of the rotating neutron star. (2) We found
that two excited modes may be both connected to vertical oscillations of the
disk, and that strong gravity is not needed to excite the modes.
