On some bootlegs, after the announcer says "On behalf of The Rolling Stones..."
a brief snippet of classicl music plays. Actually, I remember it when I was at
a LA Forum show. Any clues as to what it is?

I remember classical music before the show & after. After that show, anybody who could even think was a better man than I. Audially, SFM/JJF might sound like a dog's dinner, but seeing it live was galvanizing, esp. if you were in the front row, soaked in water & covered in confetti!