Every time I drive my M3 (DCT) at 2300 RPM and hold it there I hear a vibrato-oscillating drone that is very different from engine/exhaust sound in all other RPM ranges.
Don't know how this works but 2300 RPM in my car works out almost identically to 2nd gear at 22 MPH - 3rd at 33 - 4th at 44 - 5th at 55 - etc. Interesting.
I hear the vibrato-warble sound (which is definitely NOT pleasant) and then look at tach and speedometer and always the same 2300 RPM (+ or - 100 RPM). I do not hear it at ANY other RPM or speed.
Am I alone in this observation? Can someone please try it? Go to 2300 RPM (or the equivalent speed) in any gear and hold it there. If no one experiences this can someone tell me what it might be? I find my self avoiding this specific RPM range by shifting prematurely.
(Note: it is NOT Active Sound since I had that coded off).