However, after more searching, it sounds more like Enya "Marble Halls":
The song "Marble Halls" also made a cameo in a Svengoolie hosted film, "The Mad Ghoul"
and is also a favorite clip in PBS Classic Arts Showcase repertoire:
"I Dreamt I Dwelt in Marble Halls or "The Gipsy Girl's Dream" is a popular aria from The Bohemian Girl, an 1843 opera by Michael William Balfe, with lyrics by Alfred Bunn. It is sung in the opera by the character Arline, who is in love with Thaddeus, a Polish nobleman and political exile. It has been performed and recorded by many artists including Enya."
This choice of music is ironically appropriate for this episode b/c nasty characters embezzle money from hospital construction site and skimp on hospital structure safety to make up the difference.
imdb folks disagree:
"Yes, if you're referring to the string quartet playing in the background of the restaurant scene it is the composition called "Andante Cantible" and was written by Peter I. Tchaikovsky. It is an exquisite piece originally composed just for the stringed instruments in an orchestra. No brass, woodwinds, etc.
Through my YT channel dedicated to all genres of music, here is a recording of that song. It features the renowned cellist Yo-Yo Ma"
This doesn't sound like the clip in the background of Perry Mason scene above to me, so perhaps they were referring to a different scene, or I have bad music recognition capability.
This perhaps is the plot of a Perry Mason episode "The Case of the Prankish Professor"
"Professor Ronald Hewes teaches English at Euclid College and an exercise in observation, has someone he's hired burst into his creative class and shoot him with a gun loaded with blanks."
that illustrates how eyewitnesses, in this case earwitnesses, are unreliable and can describe the exact same event completely differently.
I feel vindicated, that the song played by the orchestra at the beginning of their repertoire is indeed "Marble Halls"
However, imdb guy is also correct, the next song the orchestra plays is "Andante Cantible":
Now, I just have to figure out the song the orchestra plays at the end of the show: