High pitched whistle particularly when night light is off, though at low volume its in the background and highly annoying. Bought the original version and thought faulty unit, sent back bought the pro, same issue, sending that back too... Engineering is substituted for design, or is that feedback intentional? who knows! dreadful for a premium product that they cannot iron out awful feedback at varying degrees depending on night light intensity. Plus instruction say comes with power adapter, none provided! This is the first review, I have left, and that's because this product is not fit for purpose, very disappointed, and I wanted to love it trying 2 of them because the build quality look good and the nightlight is a plus, but unfortunately all that effort went into that light and the design at the cost of what it is supposed to do, avoid it if you like pure sounds over aesthetics.