I isolated what is going on with the combat sounds you hear randomly, well, it's apparantly combat that is going on nowhere near your camera. Got my camera over France as the Spanish Civil War is going on and it's playing constantly, it's really, really annoying.
I think sound should play of combat if your camera is actually over it, like not even just edging the battle, but actually have the camera over it properly. Either way, the way it works now it plays the combat noises even though you're not even near the battle at all.
I have to say what I would guess is supposed to be cannon sounds is what is making that clonking noise, I thought it was just some random noise but realise now it's probably meant to sound like a gun/cannon. It doesn't though.
I recorded it in a video but I don't think I need to upload it anywhere when it's so easy to check yourself. Just start as any country, say Sweden, turn off music, zoom to France and wait for the Spanish civil war to begin and you can see yourself how it plays even though you really should not hear any.