I'm sorry for the delay. I've run a test on the line which hasn't detected a fault. Does your master socket have a test socket? If it does then would it be possible to test the router at the test socket for at least 48hrs to see if DLM makes any changes to the speed?
TT staff do not have the ability to set any DLM or profile parameters.
The normal target noise margin is 6 dB.
That is the profile that TT appears to have selected for their customers, although they did briefly offer a "gaming" profile with interleaving off, but that has now finished.
You'll just have to live with it.
The margin does seem to have reduced to 3db, However the line is capable of 60mb/s according to OR.
My speed tests are constantly hitting 35mb/s download and 13.5mb/s upload.
TT have sent an OR engineer for Friday so will have to wait and see. Rather oddly when I was with Sky I paid for 37mb and I consistently hit that speed... there is definitely something odd going on.