Combustors are contributing to the core noise emission of aero-engines in terms of direct and indirect combustion noise. The first is caused by the unsteady heat release rate, the second by the acceleration of inflow inhomogeneities, such as entropy fluctuations, at the combustor outlet or in the turbine. This work aims to investigate combustion noise generation mechanisms of a choked laboratory scale combustor by a combined experimental and numerical study. Therefore, the temperature fluctuations at the combustor outlet were determined experimentally as well as numerically and cross-checked together with pressure and OH* emission data in the frequency domain. A similar spectral content was found. Furthermore, the acoustic and entropy fluctuations at the combustion chamber outlet were evaluated for different operation conditions to estimate the direct and indirect combustion noise contributions of a laboratory combustor.