constant hum that increase as the backlight setting be increase , but even at the lowest of the three backlight setting , the hum be too loud it do not vary with the volume setting . in any case , at my bedside at night , this be the last thing I need , as it prevent I from sleep I agree with other who write the audio loop be not of sufficient quality . it would cost the manufacturer only a bit more to install higher capacity memory circuit to provide more decent audio . Iregret have buy this product .