VCDS output test strange noise?

I’ve got a B7 S4. In VCDS, when you go to Output tests, when you click start (but before actually running any output tests), something runs at the rear of the car. This also makes part of the fuel rail really cold, and you can hear the whooshing of air around it.

Now, is this the fuel pump, or is it the system pressurising the fuel tank slightly for EVAP reasons?

Any ideas clever people :slight_smile: