My 57 Focus 1.6 petrol (duratec) has been acting a little odd lately. When stationary if I press the accelerator hard then I can hear a noise which I can only describe as the sound a brush drum stick makes on a drum and then a second later the engine begins to rev as usual. If I depress the accelerator slowly then it doesn't make this noise and the engine revs slowly but normally. The car idles fine if a little tappy but can be a little lumpy when driving slowly in first gear. Changing gear from 1 to 2 and to 3 can also be a little annoying as it seems that I am not giving enough gas although I am pressing the accelerator - the car will begin to pull a second after pressing the accelerator. I have always found the fly by wire accelerator a little quirky but this issue is now making driving the car a little irritating. The car has done about 46000 miles and is about 3.5 years old. Does anyone have any ideas what it may be before I take it in to a Ford stealer?