Have a read of robertos site, in particular
this page.
Ring wire can have a dramatic impact on a poor line. Removing this on my Mum's connection completely solved her disconnection problems.
Also as has been suggested a couple of times above if you plug your modem into the test socket it should give a good idea of the maximum your line can achieve, removing any potentially faulty extension wiring from the equation.
Post the stats after doing this.
If the speed goes up a lot then you can start looking at your internal wiring as the problem.
If you can still hear noise during the quiet line test in the test socket then also as mentioned previously, may be worth reporting that as a 'voice' fault (Don't mention broadband)
Edit as didn't see the quiet line test from test socket bit
Edited by deleted (Fri 24-Jun-11 09:30:28)