The rivets in the back of mine were loose, and the whole table rocked up and down - check that it's not that. It's easy to take the table out, drill out the 6 rivets one by one and replace with bolts (do them up tight, and use nyloc nuts or spring washers so they stay that way).
If the thread is bent/wobbly itself, there are a few solutions, most seem to replace the rod with a metric one (M3 or M5) and a coupler to the Z motor, which makes it less stiff (and thus wobbles the table less). It's a bit involved, but well documented. Start here: http://www.soliforum.com/topic/2154
If you're game to try a ballscrew or something else way over-the-top, it's been done: http://www.soliforum.com/topic/2998/sd3 … all-screw/
If you've got the time, a video of the wobble would probably glean a more accurate diagnosis... Good luck!
SD3. Mk2b + glass, heated enclosure, GT2 belts, direct drive y shaft, linear bearings, bowden-feed E3D v5 w/ 0.9° stepper
Smoothieboard via Octoprint on RPi