Interference on the line

I have a phone extension with noise on the line at certain times of the day. The connections seem solid at each end so I cant work out where the interference is coming from. Do the faceplates ever go faulty / have bad connections over time due to tarnishing etc. Could the presence of lots of electrical extensions behind a desk where the new extension terminates be at fault? is it worth moving the extension? Would you rewire the extension with fresh cable etc. There was a second extension located behind a fridge thats been disconnected at the main socket but the wiring is curled up at the back of the box - could this be picking up interference from the fridge and somehow acting like a mini aerial transmitting it to the live extension (I have read about the bell wire picking up interference?

Any advice welcome

Do you have the interference at the main socket or is it just at the extension? If also at the main socket then does the noise go away if you plug into the test socket behind the face plate?