Should noise margin fluctuate massively?

I'm currently having a few issues with my downstream noise margin, it fluctuates from between an excellent 22db right down to 0db depending on what time of the day it is. Fortunately the most of the time my router somehow retains sync, but occasionally when its below 2db it disconnects and reconnects again.

Last week my exchange has a MSO and my router wouldn't sync for a an evening and the next morning. Initially when it came back on my noise margin remained at 22db but now its fluctuating wildly again.......

I've done 8 checks at different times since lastnight......

23.39 15-02-07 - 1db
00.12 16-02-07 - 2db
disconnect reported on router log 7am
08.20 16-02-07 - 9db
10.04 16-02-07 - 10db
10.33 16-02-07 - 16db
11.22 16-02-07 - 21db
14.29 16-02-07 - 4db

Its currently still at 4db.......surely there is something not right with my line??

Does seem a bit extreme. If the signal is weak (high attenuation) and you're getting a lot of pickup from the internal wiring however then it's not unheard of, especially overnight. Master test socket make any difference?

I get a constant 32db attenuation.

I don't have a master test socket either, its an old type socket with 2 phone connections in it and wires behind if you remove the screws.

The object of the master socket is to have no extension cabling connected. If the extension cables are all plugged in the front then you can achieve the same simply by unplugging them and connecting just the router directly instead. If the cabling behind includes some extension wiring then it's a little more difficult.

He could always try disconnecting the ring wires on the extension wiring - that can substantially reduce noise pickup.

Already have, made no difference.