For a few years, a volunteer named Don Murphy worked for the sound section. He was expert on recordings of opera and one evening we were discussing a project to release the Archive’s old recordings of rare opera performances on CDs.  Don was particularly fond of singers few people had heard of, and he had a good ear. The conversation that night stopped when we both realized that there was music coming from the foyer, apparently, we both thought, from the courtyard. (My office was on the balcony at the front of the building.)
‘Can you hear that?’ I asked him, a bit timidly.
‘Yes!’ he said, rather surprised. ‘It’s bloody Mozart!’
‘Good!’ I cheerfully answered. ‘I’m glad you can hear it. And it’s bloody ‘Ave verum corpus’, isn’t it?’
Don concurred, and we walked to the balcony above the foyer to discover where it was coming from. However, as we approached the low wall around the balcony, the music simply faded as if the band were moving away. We agreed, however, that it seemed to be coming from the courtyard. I told Don that I had heard it before, several times, and that it was the same each time. Though nobody else told me they had heard it, I filed it away in memory.