Possible REIN problem - whats the best approach?

Hi all
I am suffering what looks like an interference problem with my broadband.
My line normally syncs at 7616Kb with a 9dB margin. It will stay sync'ed at this at all times.
Over the last couple of days it has been re-syncing at random times at below 2Mb. The margin jumps between 1 and 28dB at this time. After a while it settles at around 28dB and a forced re-sync bring things back to normal.
About 6 months ago i had a problem where i could only sync around 300Kb. This problem corrected itself but interestingly the correction coincided with a sky van visiting a neighbour further up the road, i suspect a knackered sky box.

As the current problem is intermittent i don't think i will be as lucky this time round.
Has anyone got any sugestions as to how to comunicate the problem to the help desk. I really am not looking forward to that phone call. Are there any key words that would indicate that perhaps this is a job for BT Wholesale's SFI team.

Thanks,
Dave

PS I am now logging the linestats 24 hours a day.

First things first - any problems with the voice line when connected at the test socket?

Unfortunately not, i've tried the router in the test socket as well and the results are exactly the same. To prove it isn't coming from inside the house i ran the router from a battery and used my laptop to monitor. When the problem occurred i switched off the mains power at the incoming switch - no difference.
I am using a filtered faceplate with cat5 cable between that and the router.

It is stable at the moment and if other days is anything to go by it will be until between 2 and 4AM. I suspect tomorrow morning i will be down to 2M or less but it is pointless rebooting until around 11ish.

Dave