Observation of the constant loss contribution to the light scattering spect
ra in GHz frequency range is presented. The constant loss appears as a freq
uency-independent imaginary part of the susceptibility spectrum. It shows a
strong temperature variation. Analysis of the spectra and literature data
suggests that the constant loss can be general for many glass-forming syste
ms but it is hidden in many cases by other relaxation contributions. The na
ture of the constant loss is not clear. The possible mechanisms are discuss
ed.