Because I have an Xbox 360 slim and an Xbox 360 E 250GB (Manufacture date 2013-07-23) and the Xbox 360 E makes a 'Grrrr' noise just prior to eject and also if a game is left in the drive idle it makes the same noise after about a minute, the slim DVD drive does not make this noise.
Please see the You Tube link http://www.youtube.com/watch?v=wJp1KDXsWFQ
The DVD drive also ejects smoother on E than the slim, (that’s another reason why i think it may be different. DVD drive)
I know of one other Xbox 360 E that makes exactly the same noise.