SOLVED: land line clicking after FIOS Gigabit upgrade
Enthusiast - Level 1

For months now, we have been dealing with a persistent clicking sound on our land line phones after upgrading to FIOS Gigabit service. The technician who installed the new ONT box couldn't find a problem - pointing out that the phone connection coming from the box was perfectly clear and silent so he claimed it "must be something with your home wiring". Our home wiring has not changed, so I knew that wasn't the case. 

I've tried many things over the months - unplugging every landline phone device, and even unplugging and disconnecting power from our DECT 6.0 cordless phones. Still clicking.

Yesterday, I found the problem. Looking back at the ONT FIOS box, there are two landline output jacks (L1 and L2). We only have one landline service - and indeed connecting a phone directly there is a dialtone on L1 (no clicking) and no dialtone on L2. However, both L1 and L2 jacks were being fed to either side of the 4-wire home jacks.

It turns out that somehow, the new FIOS ONT box is causing a "feedback loop" with the non-active L2 connection. Disconnecting L2 wiring from the ONT box removed the persistent clicking. I've enclosed photos to show where the L1 and L2 phone jacks are on the ONT box.

And, as a bit of fun (and one of the reasons I love FIOS), the wired phone that I used to diagnose the problem is my 1938 Western Electric 302 (with upgraded internal network). And FIOS supports pulse dialing, so it still works on our home circuit!imageL2 (left) and L1 (right) phone connectors on FIOS Gigabit ONTimage1938 Western Electric 302