BT automated systems have screwed up my default noise margin.

[#1]

This isn't your usual gripe.
After a long battle with a noise problem on the line it finally settled down and so I asked Plusnet to drop my default noise margin from 15dB to 9dB.
After a bit of messing about (don't ask  ;D) they did just that and my line has been running happily at just over 3600kbps (ipRate 3000).
This morning I switch on my computer to find that the router has resynched sometime this morning and my stats are 4192kbps at 7.2dB. This means that my default noise margin has dropped to 6dB - last time this happened there was a very high error rate in the evening and the line lost synch - not a problem you might think except the automatic systems then decided to increase the noise margin from 6dB to 12dB 
I wait in fear and trepidation 

[#2]

You may be quite right, but isn't it also possible that your modem synced at 9dB at a time when the line was unusually quiet (hence the higher than usual sync speed) and the line subsequently got slightly worse so that when you checked it the noise margin had dropped to 7.2dB?
You'll only find out for sure by restarting your modem and looking to see whether the initial noise margin is 6dB or 9dB.

[#3]

I was fairly sure I was correct in my assumption but just did a resynch to check 4608kbps at 6.1dB (from router) 5.9dB (from routerstats)
Edit
Using routerstats I pushed the noise margin back up
Noise Margin:    9.6  dB
Connection Rate:  3808  Kbps
Much better