  Recent analyses of the WMAP 5-year data constrain possible non-adiabatic
contributions to the initial conditions of CMB anisotropies. Depending upon the
early dynamics of the plasma, the amplitude of the entropic modes can
experience a different suppression by the time of photon decoupling. Explicit
examples of the latter observation are presented both analytically and
numerically when the post-inflationary dynamics is dominated by a stiff
contribution.
