This is from a Golf manual, i refuse to buy an
ibiza one, always similar!
'1. The Central locking pump is located in the luggage compartment, on hatchback and estate models it is located on the right hand side. Before removal disconnect the battery negative lead.
2. Unhook the retaining strap then free the pump from the body.
3. Remove the insulation packing from around the pump then disconnect the wiring connector and vacuum pipe.'
Im not up on central locking, there might be a possibility the buzzing is the motor working okay, but there is a break in the piping causing no vacuum and motor noise, or it could be the noise means motor is broken. Take your pick!
Im assuming by luggage compartment they mean boot?