If you have a fixed IP Address from BT then it would be useful to set up a thinkbroadband Broadband Quality Monitor
. That will give useful info about your line even when you aren't using it.
Don't worry about the time-scale at the bottom if it seems wonky for the first 24 hours, the graph pattern should still be valid.
Re the noise margin, yarwell is probably better equipped than me to help, as you appear to have an on-going fault of some sort.
What you can do just to help your understanding is read this description
of the basic noise margin mechanism, and this page
for ways in which it can get messed up like yours.
There is a new way of getting it lowered quickly which I haven't included in there yet, but it is pointless your doing that until the fault is cleared.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost
. Internet connection -