YES! The horn! I know, it was so terrible. Luckily, my mind eventually learned to ignore it (sometimes) and I was able to get some sleep. They beep the horn as they barrel down the road like they've lost their brakes and are frantically warning everyone to get the hell out of the way. I'm in Tam Coc in the Ninh Binh province today, took a nicer sleeper bus but was only in it for four two and a half hours.