It's just the same problem that came in some Euro competition in basket-ball.
I don't remember exactly if it was in the last Euro or the previous one, but there were some country fans with horns. It was air horns, and even if I can accept some guys trying to make rhythm noise to motivate their team at the needed moment, I can't stand this continuous noise, that makes no sens at all: there is no difference between when your team has the ball, or not, there is no difference between when they need support or not,...
I supposed they initially used horns to make more noise because they are not majority in the arena, which is always the case in any international competition, except for the country where it takes place), .
For this World Cup, I suppose only South Africa fans were the one who wanted to use it, to support their country.
It's called Vuvuzela, and seems to be used in South Africa. I was surprise they did a continuous noise, but thought at first it would be only for South Africa games. Then comes the second game, and still the same noise !!!
- it looks like some South Africans are going to all the games and use the horns each game
- I saw some plastic horns (there were wood horn at first), which means fans of other countries had certainly found a dealer of cheap horns, and every fans will use it, trying they have to make more noise than the other fans

I had some pain to follow basket-ball games with continuous noise, but if it's another sport, that's another level.