Buzzing Noise at 1800rpm?
 

I know the title does not make sense, and I am having trouble in defining this, but here is the case. When I slowly increase speed, a buzzing sound (almost seems like an electric whistling sound) comes from the engine compartment direction. It only happens around 1700rpm to 2000rpm. It stops after 2000rpm.

I only does it in D. I tried it in P, N, and R, and it does not happen.

It is coming close to the end of extended warranty, so if this is an indication of an upcoming problem, I would like to get it fixed now.

It seems so interesting that the sound only happens between 1700-2000rpm. I wonder if it has something to do with transmission.

Thank you in advance for all you suggestions.

I am also getting a noise around 1700-1900 RPM - only in drive and I would describe it more as a rattle, like a heat shield (but its not a heat shield)

I can replicate the rattle when in drive, whether moving, or braking in place, and reving up to 1600rpm+

I don't hear any rattle when doing the same when in Park or Neutral.

Sounds like its coming from the mid section of the car, but difficult to say exactly.

I am speculating on it being a breakdown in the Cat, but wondering if anyone would agree, and if so, how could I inspect for this before heading into the dealer? Its a 2005 with 60K miles, so still under the Cat warranty; so not sure I am upset if it turns out to be the cat.....

On my 2005 X3 there's a rattle at the valve which can be seen by looking into the exhaust tips. This is at idle though. Maybe that's the source of your rattle.