Weird color grid on brushes

I don’t know if this belong here but i have some kinda of a graphic problem in Hammer when i zoomin to brush its shows me yellow-red grid, this is very weird becoz on other maps i make it’s not shows?
Anyone know what is this?

Screen down here

http://postimage.org/image/hdueyg7s7

http://postimage.org/image/hdueyg7s7/

topleft corner, uncheck the 3d grid box

thank you