Low-energy electron-energy-loss spectra of solid benzene and toluene in the range of the three low-lying tripler states were recorded at a temperature of 15 K. Vibronic structure within the low-lying triplet bands of toluene is observed for the first time. In the case of benzene the high resolution spectra reveal more details in the vibronic structure than known from previous electron-energy-loss spectra. With this information a modified interpretation of the vibronic structure in the first triplet band of benzene is proposed. The difference between the spectra of toluene and benzene is explained by the influence of vibronic coupling on the lowest triplet state. In addition, the systematic broadening of the vibronic levels within the first and second triplet band of toluene is interpreted as an effect of the side group internal rotation.