Have you checked the rear wheel alignment? There is about 4 or 5 mm clearance between the belt and tyre sidewall on my car and no problems with noise and the belt runs central on the sprocket. The photo shows your belt running to one side and possibly touching the sprocket outer side plate. This should give more tyre clearance not less, if it is all running in alignment. I would still try and get a new (steel) sprocket under warranty for a longer term fix.
