Really weird... My initial thought was that since it is brand new it will pass over, but reading your replies, I'm not very convinced it will, and I noticed it straight away, and have never experienced it with any other lens.
i had the exact same feeling that it was just because it was new and it would work it's way out. but my experience was that it appeared to get worse....or It just became more noticeable to me.
my fear was that if I used the lens for video the mic might pick up the sound as they can be very sensitive to any sound coming from the camera body region....if you know what I mean.
hope you can get it sorted.