Thanks for your response – I think you are onto something. What I didn't mention – because I wasn't sure it was relevant – was that after each of the last 2 incidents I "heard" songs, and I "heard" them clearly enough to recognize the songs and most of the words. So I simply concluded singing a song was part of my neighbor's wake up routine! Maybe my mind was just filling the gap. Oh well – at least I now know that I shouldn't take everything I think I hear as real.
Also, I can think of a couple of possible changes in my life which may be adding to my difficulties – a new medication, and a decline in my intake of water and healthy fluids. We'll see how it goes.