Problem with benzien consumption

Hey people have a problem I think My Clio 2 1.4l 75 ps (MTV) 109,000 km tires (195/45 R16 Hankook Ventus) “new” When I bought the car I could drive about half a tank 250-300 km, since about 2-3 weeks the tank is after 150 km half empty ??? can not explain to me why. And at the mountain from “roll” I hear a quiet bubbling/buffing between 1500-2500 rpm (MTV exhaust) that is also only for 1-2 months so. I can not explain the doubling of the consumption en, ride normally (1800-2500) U/min If otherwise it’s normal, don’t jerk or else ask for help =) Thanks a lot in advance, mfg Robin