The Dead Air Scam
For several months last year I would occasionally get phone calls and voicemails that were just a minute plus of flowing water sounds, like someone holding a phone to a river. All from central CA, all from disconnected numbers. Weird stuff!
I know what this is!!! Here's the deal:
People would get phone calls which had nothing but "dead air" - that is to say, something that sounds like it wasn't meant to be recorded. Voices at a basketball game. The sound of bees flying around by a stream. The sound of an air raid siren. People reciting strange religious texts that don't seem
quite right.
Anyway, people would pick up the phone and just listen to these sounds, sometimes having them just as ambient sound on handsfree so they could try to work out what it is.
When you called back the phone number you get some confused guy on the other end. They didn't make the phone call. What the callers do have in common is that they're all using VOIP. The VOIP numbers can be temporarily hijacked by a hacker and used for their own purposes - to send out these weird sounds.
But why? Well, in the 1960s the government had this scheme... (sorry, I couldn't resist making it sound like some MKUltra bullshit. Only for you, Agora) It was the toll free call scheme. The concept is that you don't have to pay every provider your call passes through. You pay your call provider (say viacom) and they then transfer your call through a bunch of different hardware to deliver the call. On the way, they give fractions of the call value to the service providers that provide the infrastructure.
Somewhere along the line there's some small provider who has been approached by, what the FBI believe to be, an ex-telecoms worker, who has said "if I redirect calls through your service and you give me a fraction of the value then I can guarantee profits and that people will be on the call". People hear the sounds and they stay on the call for longer than if it were silent.
Source:
Gimlet: Reply-All episode #104 "The Case of the Phantom Caller". If you want to hear something spooky - as soon as I finished writing this out the page went dead.
Automated Cold Calling
So you've got a phone call with silence on the other end. Ghosts? Vampires!? No. Automatied cold callers selling you stuff are calling you up. They wait for you to say something, then they'll transfer you to a waiting salesperson. They do this so they can save their salespeople from calling dead numbers or people who aren't home. If no salesperson is available the autodialler will hang up, and I guess they'll say a robotic "Goodbye".
Mandarin
This is just a guess, but with a bunch of people having left Hong Kong recently I'd imagine it's one of those advertising calls trying to sell some sort of migrant insurance or something. If not, wrong number.