  Aperiodic variability and Quasi Periodic Oscillations (QPOs) are observed
from accretion disks orbiting white dwarfs, neutron stars, and black holes,
suggesting that the flow is universally broken up into discrete blobs. We
consider the interaction of these blobs with the magnetic field of a compact,
accreting star, where diamagnetic blobs suffer a drag. We show that when the
magnetic moment is not aligned with the spin axis, the resulting force is
pulsed, and this can lead to resonance with the oscillation of the blobs around
the equatorial plane; a resonance condition where energy is effectively pumped
into non--equatorial motions is then derived. We show that the same resonance
condition applies for the quadrupolar component of the magnetic field. We
discuss the conditions of applicability of this result, showing that they are
quite wide. We also show that realistic complications, such as chaotic magnetic
fields, buoyancy, radiation pressure, evaporation, Kelvin--Helmholtz
instability, and shear stresses due to differential rotation do not affect our
results. In accreting neutron stars with millisecond periods, we show that this
instability leads to Lense-Thirring precession of the blobs, and that damping
by viscosity can be neglected.
