Steering wheel locks while driving?

I have a 99 catera. Recently the steering wheel has started locking up while I'm driving it. Jiggling the wheel a little bit it releases for a while but it can get a bit disconcerting. Any ideas as to what is causing it and how I can fix it? Thanks.



Edit: A little extra info. It seems to do it mostly when making sharp turns. It doesn't do it all the time. There is also a clicking noise when turning the wheel.

The clicking noise is definitely coming from the steering column. It makes the same sound as when you are turning a corner with the turn signal on and it is releasing the turn signal, but it makes it all the time. about ever 1/4 turn.