Problem Audi a3 problems with central locking



I have problems with closing (on a3), it no longer works:

first of all, it's pneumatic (I think... because it doesn't crackle when open or closed)

and after I remove the key from the ignition, the pump can be heard running for 10-15 seconds without doing anything, that is, to open the car.

do you have any idea what broke and where that pump is (it can be heard from the back left ... but I don't see anything there except the subwoofer)