I always let my car warm up at least 5 minutes for first start of the day (it's cold here). For the last month or so I've noticed a slight humming vibration type noise when I accelerate for the first time. This happens on the first acceleration only, Usually in d5 but i've heard it in reverse also. Only lasts 1-2 sec. WTF.

 

It's the VSA (or ABS) system chargeing itself. Should happen once when you first move and then again around 10MPH.

 

Thanks much CO-CL-S.