I bought a CPO 2015 M235i last summer and I reported the following:
  1. soft metallic ring (or mid-frequency metallic hum) coming from the lower half of the car; perhaps from the wheels. It only show up at low speeds; say, around 27-30 MPH with foot off the accelerator.
  2. At speeds around 75 MPH, there is a clear distinct hum coming from the engine compartment; and, again, when foot is off the accelerator.



Brought it last year and dealer could not identify the sounds. They claimed they cannot hear it. Does a bad bearing on the wheel produce this kind of sound for [1]?