pixel noise around the grass texture

I have a strange problem with my grass texture on Terrain.

In the game, above the grass texture there are some pixels noise (see screen marked on orange box).

The texture (on the left side of screen) is png, size=1024x1024, with transparency, no extra pixels on the enges.

How I can fix this “pixel noise” problem?

The problem might happen if you have the grass texture touch the edge of the image itself. Then some problems might occur. Could be because the compression is enabled. Try to shrink the grass a little bit in the image itself. You can also try to mess around with mip mapping settings.

I have found the cause. I have a few grass objects and two 3D objects (stones) - see screenshot.
If I remove some grass the problem still occurs but If I remove this two stone objects the pixel noise disappear.

HINT: If you have similar problem, try to remove some objects (one by one) to determine exactly which item cause the problem.

BTW: Grass objects are simple textures and only stone objects are 3D objects with Render Mode = Vertex Lit. I am just wondering what is the really cause of this problem. I need to take a close look at this stones objects details / settings.

Any ideas?