You should be getting around 13-14.0 l/100 km in town and 9-10.0 L/ 100 km on a trip, so clearly all is not well. The first thing to do is to ensure the spark plugs, leads, air filter, throttle body are all functioning correctly, and replace them if it's suspected they're not. Have the dealer check the exhaust back pressure, catalytic converter and oxygen sensors to make sure isn't running unduly rich or have a restricted exhaust. Look at your driving conditions, for instance, do you mainly do short runs around Ballarat that might not allow the engine to warm-up properly.

Check and adjust the park brake, they're notorious for causing a noise similar to that you are hearing.