Fuel Tank Dripping Noise

I have a 2006 Audi A3 2.0 TFSI (Golf Gti MK5 engine) I’ve had it for 4 months now and I’ve noticed it starts to make a deep dripping sound at the rear drives side of the car. It’s best heard when listening up again the fuel filler cap. When I unscrew the filler cap there’s a slight hiss and it sounds like creaking from metal inside the tank (or the tank) along with a quick whiff of petrol, the dripping sound then stops and I screw the cap back on.

It only happens after I’ve been for a drive and it can be heard from inside the car when the engine has been switched off. Is this normal because I don’t think this was happening before (unless I didn’t notice). I’ve read on some forums that it may be the pump dripping unused fuel back into the tank and others that say it’s the fuel pump controller or fuel filter.

One thing that’s changed recently is that I’ve stopped using standard unleaded Ron 95 and started using Tesco Momentum Ron 99.