The morphological vulnerability of atherosclerotic plaques, such as fluttering motion under pulsatile flow, poses diagnostic challenges in conventional fractional flow reserve (FFR) assessment. In this study, we investigate the hemodynamic impact of a fluttering plaque using a physical model of mild (40%) stenosis with and without an elastic plaque under stenotic flow. High-speed particle image velocimetry (PIV) and differential pressure measurements were employed to characterize flow patterns and pressure drop waveforms. While both models produced comparable time-averaged pressure drops, the Fluttering Plaque model exhibited extended recirculation zones, and elevated root-mean-square (RMS) fluctuations in pressure drop waveforms. The effects of the fluttering plaque on the distribution of turbulent kinetic energy (TKE) provides insight into the observed results. Our findings suggest that waveform-derived metrics, particularly the RMS amplitude of pressure drop fluctuations, may serve as novel hemodynamic indicators for detecting vulnerable plaques that remain undetected by time-averaged indices such as FFR.