Extensive LES simulations were conducted to further investigate the existence of energetic broadband low-frequency shock oscillations (LFOs). These simulations aimed to confirm previous studies regarding the presence of such oscillations. The findings of the study confirmed the absence of upstream low-frequency forcing, highlighting the significant role of downstream conditions in driving these low-frequency shock motions. It was observed that the timescales associated with these motions were approximately two orders of magnitude larger than those involved in boundary-layer turbulence. To examine the effects of varying the nozzle pressure ratio (NPR), a parametric study was carried out. This study revealed three distinct separation patterns based on the dynamics of the recirculation bubble, each associated with a different mechanism. From a qualitative standpoint, a description of the shock motion is provided, and an empirical formula based on Zaman’s (1991) approach is presented. The results demonstrate a good prediction of the main tones associated with the LFOs.