Weird almost empty behaviour

[Theurig]

I have this kind of weird behaviour with my tank. When it gets to about a quarter of a tank or maybe a little less, I hear a groan at the back towards the fuel pump, and the car goes off. At first I figured my fuel sending unit was going bad or something and giving me the wrong amount of fuel on an empty tank, but when I fill up, it stops at about 17 or so gallons meaning that there is still plenty of fuel in the tank. Also meaning that the sending unit is working fine. What could be causing this weird behaviour??