Right after you login, you should see in the middle frame all sorts of info about your router and connection. At the bottom of that page, there are two buttons. If I recall correctly the one on the left is the "Connection Statistics" (or something similar) button. If you click that, it will popup a window that lists your line statistics, such as "Noise Margin", and "Line Attentuation", both of which will be available for downstream and upstream (in that order, I believe).
See if you can take a screenshot, or at least copy and paste those figures here... Also, set the "Interval" at the bottom to 1 second (it defaults to 10 seconds), and watch your figures for fluctuation. If you notice any fluctuation, see if you can post what the figures vary from (e.g. for a few seconds your "Noise Margin" for downstream may be 10, and then it suddenly drops to 6).