Vibrational autoionization spectra of high Rydberg states of pyrazine-Ar and -Xe van der Waals clusters were observed by two-color double resonance spectroscopy. Two Rydberg series converging to the same ionization threshold appeared in the spectra of both the clusters, while only one Rydberg series was seen in bare pyrazine. One of the series of the clusters was assigned to be of "gerade," which is the same Rydberg series as that found in bare pyrazine. The other series of the clusters was assigned to an "ungerade" series, suggesting that the symmetry breakdown of the ion core is induced by the cluster formation. For both the Rydberg series, apparently very small quantum defects were involved, and the "gerade" and "ungerade" series were tentatively assigned to the d (or s) and f Rydberg series, respectively. In comparison with the bare molecule, the quantum defects of the clusters exhibited slight shifts to the negative direction, indicating the decrease of the binding energy of the Rydberg electron. The vibrational autoionization efficiency does not change upon the cluster formation, even above the dissociation threshold of the van der Waals bond. This fact indicates that the vibrational autoionization rate is much faster than the vibrational predissociation rate.