Yes, you’ll need to remove the faceplate to reveal the test socket. The test socket is the same type of socket that you’ve plugged your phone / base unit in on the front. But plugging in to the test socket is making a direct connection to the cable coming into your home. So if the filter that’s built into the faceplate is faulty in some way (or indeed if you’ve got any wiring to the rest of the house) and introducing noise, the noise should disappear when you run the quite line test from the test socket. As the sages have said, if at all possible it’s best to test using a corded phone. Wireless ones will work but they have a little bit of background noise through to start with (a low pitched hum), which may mask other noises. So not ideal but better than nothing.
