How to avoid glittering of 2D sprites in 3D view

Hi,
I am making a 3D endless runner game. To set up environment i used lot of 3D models. Because of that number of tris and verts increased. To decrease them I am trying to use 2D sprites with billboards. Everything is fine but the sprites are glittering while character is moving. The sprites close to the camera are looking good but the sprites away from the camera are glittering. I want to avoid the glittering effect. Could any one please help me how to solve this problem?

Thaks in advance.

Generally mipmaps should be enabled for drawing textures that can be drawn at a variable distance from the camera (especially far away) to avoid artifacts such as “glittering” - Mipmap - Wikipedia