Thi can happen with all ADSL suppliers - the wires between the green box and your house are the same old BT Openreach copper (or aluminium) ones that can be 40 years old or more. All they've done to give you "fibre" broadband is stick another newer green box next to the first one, this has all the various suppliers aggregation boxes in it and is linked by fibre back to the main exchange (so "fibre to the cabinet"). The bit between there and your house is the same old stuff it's always been and can have issues. Crackling on the phone line can be a sign of this.
The exception is if you have FTTP (fibre to the premises, all the way to the door) or Virgin cable.