Unstable Broadband

[#1]

Can somebody explain to me why my broadband line is so unstable? I have had it for nearly a month and sometimes it is down for several days at a time but it is almost always down for at least several hours a day. Frequently the connection will drop when we make or receive a telephone call. I have noticed that when the DSL light on the DLINK modem is down there can be noise varying from slight to severe on our phone calls.
I have jumped through loops the past month trying to get the thing sorted out. This has involved...
Moving the computer next to the master socket.
Disconnecting all internal telephone cabling so that we only have one corded phone in the master socket.
Trying several different broadband filters.
Changing the router and the cables.
BT altering the signal to noise ratio on my line??? Whatever they mean by that.
Having BT OpenReach come to my home and renew a cable on my external wall.
And still it is up and down and noisy. Why is this happening? BT keep saying there is nothing wrong with the line making me feel like a liar when I am telling the truth. Why would I do anything else? Surely BT have had this kind of problem over and over again so why can't they fix it? I am not blaming PlusNet as they have been very helpful but what are the actual reasons for my broadband behaving this way and BT saying that there is nothing wrong?

[#2]

Do a Quiet Line Test
Unplug any extention phones, extention cables, answer machines or fax (anything except the phone you will use to do the test!).
Plug a normal touch tone phone directly into the BT master socket.
Dial 17070, press option 2 (quiet line test)
You should hear 'Quiet Line Test' and then silence, there should be no pops, clicks, whistles, buzzing etc. If there is noise on the line, make sure it's not your phones connection to the socket (wiggle it about a bit) and that you are using the master socket. If you are sure its the line making the noise then dial BT (or WorldOnline) and report the fault, they should be able to sort it out. Remember that 'mis-reporting' a fault (e.g. if it turns out to be your phone, extention cord etc.) may be charged a call-out fee by BT (/WOL).
try this with the router working and not working. If there is noise on the line that will be the problem be sure to do a few tests at different times of the day it could be that BT visit and its quiet and a hour later there is noise so if you can find that there is only noise at certain times that may help BT. Look for noise in your own house which may cause it like microwave tv games consul etc.
One of the best tests is to get a cheap small radio tune it off any station so its quiet then walk neer the router and phone line you may then hear noise and could track it down this way.
I fits just noise then you should just have a dropped line and reconnect quickly be it at a lower speed unless its a very bad noise thats there for a long time

[#3]

Have I understood the following correctly?

• At times when your modem is not working, if you pick up the telephone then you hear background noises on the line. When your modem is working properly you can't hear these noises.

The next thing to try is to take the front faceplate off your master telephone socket and plug a filter into the engineers' socket that you'll find behind. (The point of this is that it disconnects any telephone extensions and home wiring, eliminating the possibility that they are causing the fault.) Plug just the modem into the filter and see what sync rate it connects at. Then plug a corded phone into the filter next to the modem and reset your modem. If the sync rate is significantly lower then there may be a fault with the filter or your phone.
Assuming the sync rate is nearly the same with and without the phone, try running like that for a few weeks. See if the behaviour regarding modem disconnects and noise on the telephone line is the same as before. If it is then have a read of http://www.kitz.co.uk/adsl/rein.htm.
If on the other hand your problems seem to have gone away (lucky you) then you just need to track down a fault in your telephone extensions.
Oh, one other important thing that you mentioned:

Quote

Frequently the connection will drop when we make or receive a telephone call.

This definitely shouldn't happen. The filter is supposed to stop the telephone interfering with the modem. You should look seriously at the possibility that your filter is faulty.

[#4]

Thank you both for replying. I have done the quiet line test and there was no noise.
I have already changed the filters several times and there is no extension wiring connected but thanks for the radio tip - that might prove useful.
I have rung up PlusNet and had a constructive conversation about the whole situation. It's almost certain that the line is generating the noise from the router signals. There is just a possibility that the DSLAM in the exchange may have a problem. PlusNet are going to talk to BT about the fault again. 

[#5]

Sounds good, I know faults are busy at the moment but we'll be able to sort it I'm sure if it is a line problem. Did the radio trick turn anything up? You'd be amazed what electrical interference your side of the router can cause.