I've recently replaced my Binatone 500 ADSL modem (supplied by Plusnet), with a BT Voyager 210 router (also supplied by plusnet).
Ever since making this change I have found that when making telephone calls on my landline, in about half of these calls the person to whom I'm speaking complains there is a lot of crackling noise on the line as I am speaking, (as though my voice is being distorted).
From my side I can hear no interference at all.
If I unplug the router from the BT phone socket and redial then the crackling is no longer present.
As far as filters are concerned, I have a "Genuine BT Master NTE5 ADSL Linebox Adaptor" which has been installed for years without any problems.......Please see here:-
Unless the router's faulty, if the wiring's set up exactly as it was with the Binatone then the only thing that would make sense would be the cable that connects the router to the phone socket. Have you tried swapping that for the old one?