The Spring/Summer 2017 edition of Desert Oracle reported on strange radio signals originating from different locations deep in the desert. But the signals were found on the AM band so not sure if it is the same thing you picked up. Here are a few of the signals mentioned in the article...
"4089 - A baffling beacon from deep within Death Valley.
4096.6 - "Kelsie" broadcasts a dash pattern from somewhere in the Mojave National Preserve.
4097.25 - The "Inyo Whopper" sounds like a choir of goblins.
6626.2 - "Rainy" makes a drip-drip sound and "Rocky" chirps like a flying squirrel.
4078 - This little robot tells the temperature from somewhere in southwestern Arizona."
The article is in Desert Oracle No. 6 but I see it is out of stock...
Could also be some other pirate radio station.