  We theoretically analyze weakly attenuated electromagnetic waves in
quasi-two-dimensional (Q2D) metals in high magnetic fields. Within the chosen
geometry, the magnetic field is directed perpendicularly to the conducting
layers of a Q2D conductor. We showed that longitudinal collective modes could
propagate along the magnetic field provided that the Fermi surface is
moderately corrugated. The considered waves speeds strongly depend on the
magnetic field magnitude. Also, we analyzed interactions of these quantum waves
with sound waves of fitting polarization and propagation direction, and we
showed that such interaction may bring significant changes to the low
temperature magnetoacoustic response of Q2D conductors.
