>> With the modem/router turned off, the phone line is clear, but as 
>> soon as
>> I turn the router on and it starts to sync the line starts to sound 
>> hissy with the occasional crackle.
 
> Very likely a bad connection in your line. Corroded metal to metal 
> contacts
> can be non-linear allowing high frequency ADSL signals to mix and 
> produce products in the audio range. 
> 
> A dirty connection with non-linear leakage between the lines can give 
> the
> same effect and is perhaps more likely to crackle but I would expect 
> it to crackle without an ADSL signal. Dirty connections are sometimes 
> influenced by humidity and are sometimes temporarily cleared by the
> higher voltage of incoming ringing. 

This is exactly the same problem I have here, and BT are very unwilling or unable
to do anything about it.

The automatic fault finding never detects a fault, and the very action of testing
the line clears the fault for a few hours/days. Ringing the line will usually clear
the fault for a while as well.

I have had a few engineer visits. They always start by testing the line and then
just announce "sorry, no fault found". On engineer told me "It's a HR fault, and
they are very hard to find", but still reported a no-fault-found and I got billed.

Another engineer did hear the fault once, and did remake some connections in the
street cabinet and in the manhole in the road, but alas the fault returned a few
days later (at least this time I was not charged).

I have, so far, successfully challenged the bill each time and got the charge
removed, but what a performance to get it done! 

All the advice given in this group on how to tackle the problem has been to no
avail as the Call Centre bods simply don't know (or don't want to know) what you
are talking about. Trying to explain the details of the fault falls on deaf ears.

The engineers usually just shrug their shoulders and say "yes, WE know what the
problems are, but can't do anything if we can't hear the fault" (or words to that
effect).

On the occasions I have spoken to BT faults department, rather than the Indian call
cent, they have never been helpful and always just take the line "well, we will
send an engineer if you insist, but if he does not detect the fault you will be
charged". As with the call centre, trying to explain the details of the fault falls
on deaf ears again.

Writing to them was also a waste of time as well. They acknowledge the letter, but
completely ignore the detailed contents and just reply with a bland "Can can send
an engineer, but you may be charged...." ect.

Eddy.