  We present a systematic study of the orbital inclination effects on
black-hole transients fast time-variability properties. We have considered all
the black-hole binaries that have been densely monitored by the Rossi XTE
satellite. We find that the amplitude of low-frequency quasi periodic
oscillations (QPOs) depends on the orbital inclination. Type-C QPOs are
stronger for nearly edge-on systems (high inclination), while type-B QPOs are
stronger when the accretion disk is closer to face-on (low inclination). Our
results also suggest that the noise associated with type-C QPOs is consistent
with being stronger for low-inclination sources, while the noise associated to
type-B QPOs seems inclination independent. These results are consistent with a
geometric origin of the type-C QPOs - for instance arising from relativistic
precession of the inner flow within a truncated disk - while the noise would
correspond to intrinsic brightness variability from mass accretion rate
fluctuations in the accretion flow. The opposite behavior of type-B QPOs -
stronger in low inclinations sources - supports the hypothesis that type-B QPOs
are related to the jet, the power of which is the most obvious measurable
parameter expected to be stronger in nearly face-on sources.
