Help with wobbly rack

I have a Salamander 5.0 and all the hardware is as tight as I can get it but will still wobble. What I think it needs is some kind of X brace to make it stronger. Any ideas?
Use two sets of L brackets and a couple of pieces of wood to secure the rack to the wall studs behind it.
A diagonal brace, from corner to corner, on the plane where there is movement, will solve your problem also. Any good cabinet maker or trim carpenter should be able to help you.