Why landline make crazy noise while hung up?

Question

I decided to ask it here because the problem to me at least is so novel that I found it curious and interesting (although I still need to fix it...)Basically, one of my landline phones on the company decided to make ear-splitting loud noises... but only while the phone is not in use, when you pick the receiver up the noises stop.I have no clue what could do that, I didn't knew a phone could be that loud (you can hear it across the room!) neither that it could make sounds while not in use.

paulrpotts · Accepted Answer

If the phone is accidentally left off the hook (or if there is an electrical problem with the wiring so that it is _reading_ as off the hook), the exchange may drive it with a very loud fast BEEP-BEEP-BEEP-BEEP sound. That's just part of how POTS (plain old telephone service) lines work. Traditionally a user would not want to leave the phone off the hook accidentally, because then that line could not receive calls, and if it was a party line, no one else on the line could receive calls or make calls.
If it stays off-hook long enough, eventually this will go silent.
See: https://en.wikipedia.org/wiki/Off-hook_tone
And: https://en.wikipedia.org/wiki/Permanent_signal

simonblack · Answer

Faulty hang-up connections. Even when the phone 'looks' hung-up, it isn't. Fix the hang-up buttons so that they work properly, or replace the faulty phone.You'll very likely find that when you listen to the phone, and work the hang-up buttons with your fingers, that the phone doesn't actually hang-up.