Stretched/blurry textures

For the last few days my textures have all of a sudden started becoming blurry stretched in places, the scales and settings of the textures are the same as usual but in 3d view they appear all stretched and ugly. Anyone else had this problem?

No, its not only in 3d view but also when the map is compiled. I have not altered any settings to the textures, which makes it confusing.

Nope, that didnt give anything. The strange thing is that it disappears when changing to another texture, but reappears when trying using the old texture again. It's definitely not a problem with the texture (wood_beam03, which isnt the only texture that isnt working, and which works in other places, completely randomly). Ill guess I'll just have to use some other textures for those brushes, then.