Crackling doesn't sound like a REIN issue, more likely a faulty joint.

Something to try. Using a mobile ring hour home number and leave the phone ringing for about half a minute. If you check the line after that and the crackling is reduced that would definitely point to a line fault (the extra ringing voltage can temporarily improve joints).

Also, have you noticed if there is any correlation between weather and what the line sounds like?

Forget broadband issue. Get the noise fault fixed on the voice side of things first.