Yup! Its where the seat buckle rubs slowly against the alcantara section. While it's great that it's not damaging leather and keeps its finish, it does creak a bit when if you move the seat slightly either when your weight shifts or using the clutch.
Hopefully I have the solution for this as it happened on mine too.
Sit in the seat and clip your belt into the fastener. Now look at the fastener and you'll notice that it contacts the side of the seat bolster. Get a bit of black sticky back felt (they come in little packs of squares) and put it on the fastener where it rubs. If you do it neatly you can't even see it.
To test if this is the actual problem just put a cloth there temporarily while you're driving - if the sound disappears then you've cracked it...