Noise damped modes for the Plummer model. Upper panels: overdensity maps at the orbital plane using BPM (top) and PM (middle). The wake and the overall map are affected by noise in the PM test. Bottom panel shows the APS (green lines), where the ℓ = 3 peak is severely damped for the PM code (dashed line). Both codes use 512³ cells, 128³ particles, and a spatial resolution of 1 kpc. Additionally, we include a PM case using 256³ particles (magenta dashed line); the APS amplitude is greater than the previous test. The dependence on particle number suggests that there is a shot-noise effect in the PM APS.