When i got the bike, the fuel light/bars used to come on when there was about 3 litres left in the tank (about right). Lately, it seems to be coming on earlier and earlier (not going by km's ridden, but how much fuel i'm putting in). Today it seemed to have come on when i had used around 13 litres (meaning 5 left in the tank). My fuel consumption based on l/100km has stayed almost constant, but the number of k's before the light coming on has gone down. What could cause this? Could the sensor in the tank have moved somehow?