I know it wasn't supernatural, you said it was physical...
Did he hear a typical sound like a squeak, or a bang or a click, or was it specialized, like a conversation or the conductor saying something?
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)