A lidar system includes a light source configured to produce a beam of light, a scanner configured to scan a field of regard of the lidar system, and a receiver configured to detect light from the beam of light scattered by a remote target. The scanner includes a polygon mirror having a block with a first wall, a second wall, and several reflective surfaces angularly offset from one another along a periphery of the block, the polygon mirror configured to rotate about a scan-mirror rotation axis to scan the beam of light across the field of regard. The scanner further includes a bracket adjacent to the polygon mirror, where at least one of the polygon mirror or the bracket includes a noise-reducing feature configured to reduce acoustic noise produced when pressure waves generated by the polygon mirror during rotation are incident on one or more components of the scanner.