No, he hears the low thumping, rumble before anybody else. Otherwise he'd be warning the docs before the military ambulances pull into camp as well.
I live very close to a Marine airfield and every time a helicopter or an osprey approaches in the distance, in my best Radar voice, I mumble, "choppers...".
Usually when I have guests, they would look at me and say, "huh?".
To which I reply, "Give it a minute, it's the neighborhood watch on patrol..."
Sure enough, in a couple of minutes, the windows are rattling as they pass just a few hundred feet above and my guests are flying out the door with their camera phones.
I think Radar purportedly did have some kind of ESP because he would often walk into the CO's office (especially Blake's) with papers the CO was just about to ask for. He'd also start saying something the CO was about to say. Another funny Radar meme was how he'd be standing right behind Blake just before he was summoned; Henry would yell "DON'T DO THAT!", LOL