Disconnect when phone rings + Crackly line

[#1]

We are getting short disconnects when the phone rings. Games get kicked out. Connection light on DG834GT goes briefly orange.
I've tried changing both the microfilter on the modem, and the one on the phone with no improvement. The modem was new (replaced the old one due to it giving very frequent disconnects which started just over a week ago.
I've just checked, and the line does seem to be noisy (continuous quiet hiss with the odd crackle) when listening to the handset, but I cannot be certain it hasn't always been like this.
Current stats:
ADSL Link Downstream Upstream
Connection Speed 5920 kbps 448 kbps
Line Attenuation 16.0 db 10.5 db
Noise Margin 20.9 db 11.0 db
This is just after the latest reconnect (when I phoned from my mobile to check what was going on). Previously it has been at about 7600 with 15dB noise margin. Prior to the connection problems, it was a solid 8000+ (Ie max speed)
I'm now wondering if the disconnects with the old router were due to the same problem.
Any Ideas?
EDIT: Mrs C has just confirmed the crackly line is a new effect. I'm going to run through the fault checker and raise a ticket.

[#2]

It sounds like a line card problem - at least that was the reason I was getting the same problem
If you can hear noise on the line when the router isn't connected you should report it as a voice fault

[#3]

Confirmed - line crackles with router disconnected.
What is the best way to report the voice fault?

[#4]

Call your phone supplier - BT or Plusnet and ask them if they can hear the noise - if they can you are 90% there
BT have a specific voice fault number 0800 800 151 and for Plusnet it is 0845 140 0080 which is also free
Oh - don't mention broadband if it is BT

[#5]

Phoned a very helpfull chap at BT
He could hear the crackling - which after a series of tests had me plug the phone into the master socket - crackling is now apparently gone. Will be monitoring for 24 hours then he calls me back.
If it is OK during that time - then it looks like something internal, and I've got some diagnostics to do.

[#6]

OK - annoyingly, the line was fine for 24 hours. So I've plugged the phone back into the extension - and there is still no noise. Will be checked again tomorrow night.
But the BB still disconnects occasionally when the phone rings.

[#7]

Even if the BB doesn't disconnect when the phone rings it is very likely that the noise margin may jump all over the place. I suggest you check if you can see that when the phone rings with the phone in the extension. If so plug the phone and router in to the same filter and plug that in to the test socket inside the master socket and then check if you can see the same effect (using the test socket disconnects the extension wiring).
Check this with both filters.

[#8]

Quote from: tonycollinet

Phoned a very helpfull chap at BT

Did you get his number - will you be able to get him again !  ? 
To be fair BT do have lots of very good staff - I worked on projects with several.

[#9]

Quote from: jelv

Even if the BB doesn't disconnect when the phone rings it is very likely that the noise margin may jump all over the place. I suggest you check if you can see that when the phone rings with the phone in the extension. If so plug the phone and router in to the same filter and plug that in to the test socket inside the master socket and then check if you can see the same effect (using the test socket disconnects the extension wiring). Check this with both filters.

Sadly I don't have a test socket - only an old style master socket. Will try your suggestion though, using that.