ssue with fillng petrol tank

Hello there! I'm having an issue filling my '99 2.4 A4 Auto at petrol stations. Despite the tank being empty, the pump clicks off as if the tank is full, only this happens rather frustratingly every litre or so - so it's taking me several minutes of repeatedly pulling the trigger on the pump to fill the tank. This is my third A4 (I had a '97 1.8 SE and also an '01 S4 bi-turbo) and this is the first time I've ever exeprienced this problem - the car has done it ever since I picked it up 2 months ago. I spoke to my local garage, but they were reluctant to start charging me for pulling the car apart when there is apparently so many things it could be and would mean taking it to and from a petrol station to see if they'd successully fixed it. Can anyone suggest what might be causing this? Has anyone else had this problem? It's driving me mad!