Many kinds of IR and millimeter wave components, e.g., distributed feedback lasers, filters, etc., are based on layered periodic structures. The latter are known to support electromagnetic waves guided by separate layers (waveguide modes) or interfaces (surface modes), as well as by the spatial period d of the superlattice (Bragg-type modes). Besides of these, there exist special bulk modes which can be described as plane electromagnetic waves in an effective homogeneous anisotropic medium . Theoretically, the dispersion branches of these excitations are subject to change in the presence of dc magnetic field resulting in the tunability of electromagnetic wave power transmission . However, there are little experimental data on the transmission line shape, particularly at the bulk mode resonance minimum which have been found to be very deep. Present experiments have been carried out by using high dynamic range technique revealing an unexpected additional line.