We've had a knocking in the front of ours for about a year. Got new tires put on last week and had them check the suspension- front left lower control arm bushing shot. You can get new ones for about $20 at napa if I remember corretly. I do not, however, know what it takes to replace them. I am going to do it when I replace the shocks in a few weeks so I will have the front torn down already.

If I find anything I will post it.