BT don't like manually specifying the noise margin... if the line has a lot of errors they will apply some cap of some sort thats about it...
If your still getting problems then the best thing to do is ask them to reset the line management (DLM).
Other than that - if your router allows it you could tweak the SNR with say DMT Tool or telnet... depending on the router model.
Edited by deleted (Thu 25-Jun-09 02:29:46)