>> I've tried the quiet line test and all I get is a voice going 'quiet line test' and a load of hissing and crackling. I take it that the line should be totally silent.
Correct. The fact that you can hear noise during this test indicates a fault on the telephone line itself.
The hissing and crackling indicate resistance on the line, possibly caused by oxydisation of the joints or water etc.
>> They also say that since the fault is with the broadband it's not their problem
See my post above - as soon as you mention adsl then they try and fob you off back to the ISP.
You are now in a horrible loop because of what weve just round out/confirmed, if you explain all this to your ISP then they will say its an actual line fault and needs a BT line engineer rather than a BT adsl engineer.
>> if they send an engineer out and he finds no fault they will charge me £150
They legally have to warn you about that - so you have to be prepared and make sure that the fault isnt with any of your own equipment. Check from the master socket, check that its not a faulty filter - because this could also cause similar symptoms.
Try the quiet line test from the master socket without any other equipment plugged in - if you can still hear the hissing then, youve done practically all that you can to eliminate that its not your own equipment.
151 is really the correct place where you should be reporting this type of fault. Unfortunately the people on the end of the phone dont understand how the actual systems work and as you are correctly trying to explain your findings as soon as you mention adsl then they close their ears "not our problem".
As long as you have done all that you can to eliminate that the fault isnt in your own equipment then you should be ok when the BT engineer arrives. He will be more astute to these kind of problems. The offer of tea and biccies whilst you explain what youve done re the quiet line test. Explain that your adsl only works when the line is being used and "could there be the possibility of a high open fault".
If you dont get any joy with BT direct then the only course of action would be explaining our findings so far and hopefully they can pull out the stops on this one. Not sure what the foreign call center at Be* are like Im afraid.
>> What about my suggestion of getting a new phone line installed?
They may well work, but you will have associated costs with that one too for the provision of both the new line installation.. and provision of adsl on the new line.
Obviously I cant say for sure because I dont want you lumbered with the £150 fee.... but if I were you, I'd go along the "performed all the tests I can here" BT route on 151. Then offer tea to the engineer when he arrives