The side to side play, if over spec, is likely due to either tie rod ends or the steering rack. The rattle could be due in part to this, but a look at the rear shock mounts is advised - the parts get separated and you get a rattling sound right behind the back seat. This would also be a good explanation for the clunk sound. Usually this happens on the passenger side because of rougher, high-wear pavement nearer the roadsides.

If this turns out to be the problem, this might be a good time to change the shocks, too. No doubt you've lost the little collar that keeps the shock cannisters from touching (another source of rattling).
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David
1998 S70 T5SE // misc mods (mostly lighting) // red calipers // Michelin Pilots
1992 940 GLE//SilverStars//Hella MicroDE