[*bimmervibe]

I recently purchased a 2015 228 xdrive with automatic transmission. I love the car but I hear a subtle drone/vibrato noise coming from the engine at 1k rpm in any gear. The noise disappear at lower or higher rpm. The car is still under warranty and I explained the issue to my dealer. They tried the car and said it was perfectly normal. Anyone experiencing something similar?

Now I also noticed a similar noise when accelerating full throttle, the noise can only be heard from 50 to 55 mph. I can't hear it cruising at that speed. No apparent vibration either. What could it be?

Thanks for any input.