Fluctuations are observed in the recording of any process parameter in a nuclear reactor even when operating at full power and steady-state conditions. These fluctuations (also called noise) are due to, for example, turbulence, coolant boiling, mechanical vibrations, etc. The monitoring of those parameters allows detecting, using existing instrumentation and without introducing any external perturbation to the system, possible anomalies before they have any inadvertent effect on plant safety and availability. In the proposed work, the time-domain PARCS code was used to model the effect of stationary perturbations in nuclear reactors. The results of such simulations were compared to the results of simulations performed in the frequency domain using the tool developed by Chalmers University of Technology called CORE SIM. The development of a few test cases based on a real reactor model were undertaken in order to compare the time-domain and the frequency-domain simulations. A methodology aimed at comparing these two different types of tools was established. It was demonstrated that PARCS, although not primarily developed for such calculations, can reproduce neutron noise patterns for reasonable frequencies. Nevertheless, it was also observed that unphysical results were occasionally obtained.