A method of assembling and retaining a noise attenuation device (30) within an air inlet (16) of a compressor cover (12) includes inserting the noise attenuation device (30) into the air inlet (16) and applying a rolling compressive force to the air inlet (16) using a forming tool (40). As a result, the air inlet terminal end (17) is deformed radially inward so as to form a radially-inwardly protruding lip (17b) about the air inlet terminal end (17). The radially-inwardly protruding lip (17b) is configured to retain the noise attenuation device (30) within the air inlet (16). The forming tool (40) used to form the radially-inwardly protruding lip (17b) is also described.