That trick with a blade of grass is real and there's nothing spooky about it. What you're hearing is AM broadcast from a nearby transmitter. The blade touching rusty metal makes a tiny point contact, and rust plus moisture behaves like a crude rectifier. That's the same principle as the old crystal radio. The rectified audio is what you hear pressed against your ear, and the big metal object it's attached to is doing the antenna work. Want to try it yourself? Find a long run of metal, chain link fence, metal gutter, a kids' swing set, anything tall and grounded. Late evening works best when AM stations are pumping out more power and there's less static around. Pull a fresh blade of grass, hold it so one end touches the metal and the other end sits against your ear canal, close your ear with a finger so the sound doesn't leak out. Tune nothing, you don't get to pick the station, you get whatever's strongest nearby.
If you hear nothing, try a diffrent spot on the metal. Rust texture matters a lot, so move around a few feet. A dry grass sometimes works better than green. Don't expect FM or music quality, it's mostly talk and murmur. Honestly this is how a lot of old hams got hooked as kids, and half of us ended up building crystal sets because of it. If you want the proper version of this, wind some enamel wire on a cardboard tube, add a diode and a high impedance earpiece, and you'll get real volume without pressing your head against a fence.