Unfortunately you're unlikely to see any speed increase with the speed boost as your router is syncing at a lower speed than 40Mbps (the line wouldn't get replaced)
Do you still hear the noise with just a telephone connected, no router?
Have tried various combinations and I do notice more of background static sound on the line when router is powered on.
Tried phone lead direct into test socket (no filter), via a microfilter direct into test socket, and with filtered face plate back on.
As sync has improved I'll wait and see if it returns to its previous rate nearer summer time. As I was getting 40,000 kbps back in November, but rate now seems restricted to 34,999 kbps with no change in 7 days.
Thank you for your combined responses. Been appreciated.
For future reference I'll leave comparison picture below.
Been meaning to post this for a while, for future reference purpose.
Issue was resolved after TalkTalk telephone support contacted me and agreed to book an Openreach visit in March. The engineer replaced the line from the black cylindrical gel filled box to a new terminal box inside doorway. And I found out the internal cable was aluminium wire too. Once the work had been done the disconnects stopped and speed recovered in a few days.