sudden drop in speed?

Hi,
Been on Demon Internet's 2mbps service using an Eicon Diva 2480 wireless router (some Alcatel chipset-based thing), up until about 3 weeks ago, when I was upgraded to their 8mbps service.
Download speeds have been varying, but on the whole, it's been 300~400k/sec which I was happy with, until a couple of days ago, it dropped dramatically to around 30~50k/sec.

Router tells me the following info:

STREAM STATISTICS DOWNSTREAM UPSTREAM
----------------- ---------- --------
Data Path Type : INTERLEAVED INTERLEAVED
Current Bit Rate (kbit/s) : 7616 448
Attainable Bit Rate (kbit/s) : 8278 746
Attenuation (dB) : 32 18
Noise Margin (dB) : 9 21
Output Power (dBm) : 20 11

(sorry about the formatting..)

From reading other posts here, I realised that 32dB Attenuation is a bit noisy, so I grabbed another router (some generic no-name with a Conexant chipset), and the Downstream Attenuation hovered between 8 and 12dB, but there was no inprovement in speed.

I played around with TCP Optimizer, tried another PC, changed filter and dsl cable to no avail.
The only thing I havent done is take the face off the master socket and plug into that, since its under the floorboards alongside all the dirt and spiders..

Should I try this before yelling at Demon and/or BT? or is there's anything else I can try?
THanks for your time ;o

a noise margin of 9 is pretty good, looks like the line is OK but maybe the IP profile (BRAS profile) isn't.

See if http://test.speedtester.bt.com:50301/ is working and it will disclose your IP profile.

bizzare. Things started to speed up a while ago for no aparent reason, and I'm outside the so-called 10-day settling period.
Anywho, did the speed test and got the following:

IP profile for your line is - 6500 kbps
DSL connection rate: 448 kbps(UP-STREAM) 7392 kbps(DOWN-STREAM)
Actual IP throughput achieved during the test was - 3265 kbps

Only other thing worth mentioing, is that when the router starts the PPP service, it connects to one of two servers. Maybe one of them was having issues for a couple of days??

the PPP session may be going down one of two or more pipes with variable traffic loads, you may have landed on a less busy one. Nothing stops after the 10-day period.