  We propose a novel mechanism for the production of gravitational waves in the
early Universe that originates from the relaxation processes induced by the QCD
phase transition. While the energy density of the quark-gluon mean-field is
monotonously decaying in real time, its pressure undergoes a series of violent
oscillations at the characteristic QCD time scales that generates a primordial
multi-peaked gravitational waves' signal in the radio frequencies' domain. The
signal as an echo of the QCD phase transition, and is accessible by the FAST
and SKA telescopes.
