What's the condition of the BT line like, any background noises when making phone calls?
Try `BT line Test Facilities' (use a wired phone, not cordless)
- Dial 17070 on the phone, you should get through to BT line Test Facilities.
- Then Choose option 2, Quiet Line Test
- At this stage you should hear absolutely nothing. It would help if you pressed the 'Secrecy' button on your phone as your phones mic may introduce noise.