Fibre - upstream speed drop

[#1]

My upstream sync speed has 'plummeted' to exactly 17000 kbit/s, this has always previously been the full 20Mb. 
It looks like my upstream has been put on a banded profile as my modem/router is showing Send direction Max. DSLAM throughput 17000 (and Min. 8000).
I'll apologise right now to everyone who'd be happy enough with 1/20th of this upstream as I don't want you to think I'm moaning about 'only' getting 17000 upstream or complaining that it's actually affecting my internet in any way - the question is simply does this indicate a potential line fault?  Having had 20Mb for around a couple of years and always having had an attainable upstream well in excess of 20Mb/s (has been over 30Mb/s, currently still showing over 25Mb/s) it seems odd that the DSLAM has decided to act in such a sudden manner unless something on the line has changed.
Is there any point in raising a fault or should I leave it a while to see what happens?

[#2]

Hi w23,
Looks like it's been done by the DLM system, though I'd guess more for errors seen than drops as there's only a couple showing on your connection log:
<img src="http://community.plus.net/visualradius/generated/image13898868885074.png"/>

Though it's possible it could have happened as a result of one of those in the early morning. I'm afraid I'd not recommend raising a fault though as that kind of drop wouldn't be seen as a fault by our suppliers and the upstream is still working at a very good speed. Hopefully it'll stay stable (possibly even improve) and the profile will be updated accordingly.

[#3]

Thanks Matt, stability is not an issue, and performance is best described as 'perfectly adequate', only my monitoring stats show anything amiss to be honest.
I guess there may be increased noise on the line so DLM has capped things to limit errors (still getting a few - 0.06 average CRC per minute since syncing at 17000 some 16 hours ago).
I'll just monitor to see if things deteriorate (or, indeed, improve)