Some suggestions are:
1. You have an issue with your extension wiring. Try the test socket...
2. Line fault... Try a quiet line test. Dial 17070, option 2. Any buzzing or crackling then report as a phone line fault
I hope these suggestions prove useful?
Never attribute to malice what can be adequately explained by stupidity
Edited by noinchki (Tue 13-Jan-15 14:18:16)