Multiphoton ionization time-of-flight mass spectroscopy has been used to study heterogeneous cluster ions containing NO and ethene. As previously noted in the literature for other NO clusters, NO-ethene heterogeneous cluster ions show a tendency to form even-electron species. In addition to this effect, we also observe a number of ion-molecule reactions that occur within the heterogeneous clusters. These reactions lead to cluster ion series which contain new molecular species. Deuterium isotope experiments explicitly indicate that both CH4 and NO2 are formed as cluster ion products. We speculate that the methane formation occurs via this reaction within the photoionized cluster: {C2H4}(m+1){NO}(n+1){NO+}--> {C2H4}(m){NO}(n){CH4+} + N2O + CO.