  We investigate the low-frequency wave mode associated with heavy particles
and its instability in a collisional complex plasma with drifting ions. The
effect of the ion drift on the sound velocity of this mode is discussed. The
general condition of the instability is derived for subthermal ion drifts,
taking into account strong coupling of the particle component. As a general
tendency, strong coupling effects reduce the sound velocity and facilitate the
occurrence of the ion drift instability. A wide parameter range is considered
from the weakly collisional to strongly collisional regimes for the ion and
particle components. The chosen plasma parameters are representative to the
PK-4 experiment, currently operational on board the International Space
Station.
