Dreamt I was tuning a piano that kept growing new keys

I keep coming back to this one. I'm on a street corner that's also a riverbank, and the piano keeps sprouting extra keys every time I think I've got it in tune. The weird thing is, the crowd isn't annoyed — they're swaying along, and the wrong notes sound like rain on a tin roof. Woke up humming a chord I've never heard in real life.