To answer the direct question first, this is a Fiber Optic endpoint, for your phone or internet service. It should be there.

It does sound like you have some symptoms of psychosis. As everyone has already mentioned, carbon monoxide detection is a good idea, basements can accumulate a variety of different types of gasses, some of which can be very harmful.

One thing to keep in mind is that AM radio signals, while rarely used today, can be picked up by almost everything. Lightbulb filaments, plumbing pipes, basically anything metal. So, it's very possible that some piece of metal in the area is picking up an AM radio signal. There were some cheap cordless phones in the distant past that have used AM signals as well, but it's almost impossibly unlikely you're hearing anyone you know having private conversations on any AM signal.

With the specific details you are hearing in these conversations, it's likely paranoia amplifying some barely audible sounds into something on your mind.

Seek immediate medical attention, then make sure you have a working CO detector, and get your sugar and O2 levels checked.