Wasn't this solved awhile back?
My recollection was BMW has stopped installing bonnet liners to increase engine noise. Cars of late should definitely not have any. Around the middle of the year some cars were still coming delivered with liners as BMW makes the car bodies in advance, and depending on colour demand a body can be a number of months old before it slips back into the production line.
I'm sure that was the answer on here, or over on babybmw.net.
Current: 135i Auto, Le Mans Blue - w/ Bridgestone RE-11 rears, GP Thunder 7500k angels, & "golf tee" mod plus a few M3 suspension bits and pieces...