I've got a my99 wrx ra import , which has got a standard 5 speed box , every time I change gear at high revs it grinds before going into gear

low revs seem to be fine and just plodding about its ok but as soon as I get it up near the red it hates changing gear

I know the five speeds ain't great but it's not like I've got 500 bhp under the bonnet as she is pretty standard

any one know what's happening?

 

syncro goin, same as mine