A compressor has a housing assembly having a plurality of ports including a suction port and a discharge A male rotor is mounted for rotation about an axis. A female rotor is enmeshed with the male rotor and mounted in the housing for rotation about an axis for drawing a flow from the suction port, compressing the flow, and discharging the compressed flow through the discharge port. A cavity group is between the discharge port and the male rotor and female rotor. The cavity group has a first member separating a plurality of cells and a foraminate cover member atop the first member.