Steering rack fixing

[DRCorsa]

I have fixed my steering rack to the chassis with those aluminum brackets but it seems that the rack has a rather measurable play, it's not rigidly fixed on the rack support. The aluminum brackets are rigidly fixed to the rack support, so the play is between the rack and the ally brackets. What could be the prob? I will try to upload a small video clip to show you what i'm talkin about, but until then any ideas?