Having listened to static for long periods of time before, it's difficult, but not impossible to tell when you start having auditory hallucinations. It simply doesn't fit the correct patterns of proper voice and your brain is filling in patterns and frequencies that simply aren't there. But....

Our atmosphere is filled with tons of human generated RF. Given the correct conditions, you could hear signals bounced all the way from the other side of the earth. (That is a thing in amateur radio, actually.) On a really good day and if I am in the right location, I can use a simple 5-10W handheld radio to key ham radio repeaters hundreds of miles away. It's rare, but it happens.

When you realize that everything electronic has the possibility of making noise and that everything metal is an antenna, hearing real random voices in the most random of places is absolutely possible. With enough time and motivation, you could probably make the capacitor or inductor whine on an old GPU produce music or even voice.

If there is any kind of signal in random noise, it's super easy to spot with graphical spectrum monitors. Matching audio with visual queues is almost a sure way to avoid just "hearing shit".

There is also a ton of absolutely bizarre things people transmit. You could probably search on YouTube for strange radio transmissions and be occupied with that stuff for months. If anyone can make any kind of noise, it's been transmitted or is currently transmitting from somewhere.

These are built-in to many rigs nowadays: