Had the same thing around 15K, dealer topped it off for me. Haven't had any problems with it since then.
F30 335xi | MSport | Estoril Blue | Sport 8AT | DHP | 19" 403M | ZDA | ZTP | Sat radio | 494 (Gone)
F30 335xi | MSport | Estoril Blue | 6MT | DHP | 19" 403M (Gone)
E92 335xi | MSport | Le Mans Blue Metallic (Gone)