Thanks for replying.
Watching the graphs in Routerstats this morning the d'stream margin margin stayed very stable for about 30 mins varying between 15.2 and 15.5db.
When i turned on my computer this afternoon I discovered that my router had lost sync earlier with the speed now at 5,952 and the d'stream noise margin 13db. Observing my line stats in routerstats the margin remained relatively stable for 30 minutes at around 12db before a brief drop to 8db. A couple of minutes later it dropped again to 8db, rose to 16db and then dropped to zero losing sync at 1:55pm. The line resynced at 5,504 with a d'stream margin of 15db and for about an hour showed little variation other than a very very gradual downward trend. Then between 3pm and 3:30pm it dropped twice from 14db to 12db before rising again to 14db. There was once again little variation until about 3:50pm where there was a couple of minutes of erratic activity with the margin falling to almost 10db, rising to 15db. dropping to 11db before settling down again around 14db.
When I have run RouterStats in the past (long before these problems started) over the course of an hour the margin would often fluctuate between, say, 5db and 8db with occasional drops as low as 2db and peaks of 10db.
Observing the graphs today there is a very different pattern with far less overall fluctuations than before the problems started- this morning it even remained between 15.2db and 15.5db for half an hour.
It seems there are long periods of stability followed by sudden small spikes and occasionally much bigger ones (like the one at 1;55pm.)
Does anyone have any thoughts on this?