Please have your main bearings checked.
I had this problem at around 3000 miles.
These are the symptoms:
-Only hear it when your oil temp is ~170F or above
-It changes in frequency as you rev your engine to 1.5k or 3k rpm in neutral
-Drive in the highest gear at 25mph in a very quiet street and roll down your windows you can still hear it
If all above is correct get your main bearings replaced! Your car will be in the dealer for ~5 weeks! Good luck!