The permeable surface form of the Ffowcs Williams-Hawkings equation provides an efficient basis for predicting helicopter rotor noise when the flow over the blades is transonic. It requires knowledge of the temporal variation of fictitious acoustic sources over the permeable control surface. Calculation of these using unsteady computational fluid dynamics (CFD) solvers is feasible for straightforward helicopter motion, but becomes prohibitively time consuming for more complicated maneuvers. Low-order modeling provides an efficient alternative. Because at transonic speeds significant noise originates at the shock surfaces, low-order modeling of the two-dimensional shock dynamics was first performed to provide an insight. Using data from CFD simulations, system identification, a modeling technique suitable for dynamically linear systems, was performed. The position of a well-formed shock was found to respond to variations in blade speed and blade pitch angle with approximate first-order lag relationships; these findings were consistent with harmonic tests. Low-order modeling of the acoustic sources was then performed, although for simplicity attention was restricted to two-dimensional motion and an acoustically compact control surface. Models were obtained, again using system identification, and were successfully used in noise prediction. Analytical consideration of the sources revealed that their dynamics arose mainly due to the shock motion. These findings serve to demonstrate the potential of low-order modeling in predicting transonic helicopter noise.