The Elder is saying that the sand storms above ground is made by them so they can go out undetected, but i have never seen a sand storm in hidden valley??

Can this be fixed???

It's just a lot of wind, darkened skies, and a bit of dusty swirls of foggy-looking sand swirls. I don't know why you may not be able to see the effect (like as you approach Hidden Valley the sky/light darkens) unless it has to do with video settings, but you're not missing too much. I think there are times when the effect isn't as strong (daytime perhaps), maybe you just haven't been there at the right moment.

Sandstorms in Hidden Valley only happen at night. Try waiting till night-time.

Well think it would be a nice effect to have the sandstorms appear all the time there, would make the place a bit more exotic.