We spoke a couple of days ago and you mentioned to report back any further issues on this thread.
Just to say that the intermittent crackly line problem raised its ugly head again this morning (Sat 10 June). I experienced several disconnects and the crackly line problem between 10am and 12pm. Tried quiet line test using wired handset in test socket and there was definitely crackle on the line. Broadband speed dropped from 40/7 to 17/0.195. I manually rebooted the router at 12.32pm and speed has now been restored to 40/7. I have screenshots from the homehub status page - showing the drop in speed and its subsequent rise - should they be required. Speed was confirmed using http://speedof.me
I tried using the BT troubleshooter page and it did not detect a line fault or a broadband fault. Couldn't get the speed test to work as it kept saying that it could recognise my device as being attached to the router, not sure why that is the case as it was connected directly by ethernet to port 4 on the router and it was the only connected device.
This is basically the same thing that has been happening for several months albeit it now seems to be less frequent and when it does occur less prolonged than it has been in the past.
For info other dates/times I have noticed the same problem over recent weeks are as follows. I suspect there will be other occurrences, these are just the ones that I have noticed.