Is it a beeping noise? It might be the Guy's and St Thomas shuttle bus reversing. Since they moved the stop from the East side of New Hunt's house to the Guy's campus side, every bus has to reverse into position. One bus in particular seems to have a much louder reversing beep than the others. Although I must admit, for me anyway, like the constant hum from Guy's generators, it has blended into the background and no longers registers with me.