So I've noticed for a while that the ZF 10 speakers tend to make a humming noise when lower tones need to be produced. I don't "feel" the phone vibrating as some apparently have experienced, but it is kind of bothering now and then. It happens at around 115Hz and lower (you can test this using a frequency generator app). Mostly when streaming video, not so much when listening only to music. Or less noticeable to say the least. Is this a design/engineering mistake? Or do they intentionally designed it to hum/oscillate the sound wave to emphasize lower tones? Anybody else had this experience? If so, how much does it bother you?
