  We study possible mechanisms of excitation of quasiperiodic oscillations in
the accretion flow of black hole accreters in their hard spectral states, in
the context of the `truncated disk' model. Quasi-spherical oscillations of the
inner ion-supported accretion flow (ISAF) can be excited by the interaction of
this hot flow with the cool disk extending outward from it. The fundamental
mode of (p-mode) oscillation is most easily excited, and has a frequency near
the Kepler frequency at the inner edge of the cool disk. The strongest
excitation mechanism is a feedback loop involving cooling of the ISAF by soft
photons from the cool disk and heating of the cool disk by the ISAF, while
synchrotron emission can be a relatively strong damping effect. Growth times
are computed by detailed Comptonization calculations of the interaction of an
idealized ISAF with a cool disk. Typical growth times as short as a few
dynamical times are found, while amplitudes can be as large as 10%.
