Season 7, episode 5.
Original air date: 18 November 1956.
Cast: Jack Benny (Jack Benny), Don Wilson (Don Wilson), The Sportsmen Quartet (Themselves- Singers), Eddie `Rochester` Anderson (Rochester Van Jones), Gisele MacKenzie (Lucky Strike Commercial), Gurney Bell (Member; The Sportsman Quartet: uncredited), Bill Days (Member; The Sportsman Quartet: uncredited), Robert Garsen (Member; The Sportsman Quartet: uncredited), Morgan Jones (Officer Kerry: uncredited), Martin Sperzel (Member; The Sportsman Quartet: (uncredited), Robert Stevenson (Officer O`Hara: uncredited) and Lyle Talbot (Sgt. Vandermeer: uncredited).
The Sportsmen Quartet sing `Top Hat`.
Per the title, the Maxwell was a gag on the Jack Benny radio show. The Maxwell was an antique car even in the 1930`s. The sound effect of the car was made by Mel Blanc which was always on the verge of collapsing with a `phat-phat-bang`.
From IMDB.
From IMDB.

A shame there are no cast credits here. The voice of the officer who found the Maxwell is Herb Vigran.