Green’s Dictionary of Slang

chamber music n.

[pun]

the sound of a chamberpot being used.

[UK]‘Doss Chiderdoss’ ‘With Music’ Sporting Times 8 Jan. 1/3: They answered ’er back in rude terms, I confess / [...] / And made ruder reflections — with music? Oh, yes! / I suppose ’twould be called chamber music.