Yeah, I kind of had something similar happen to me this spring. For several months I had a knot in the left side of my lower back/upper hip area. I attributed this to putting on some jacked up gear (at least boss briefs, sometimes a suit as well) and going for broke every week on squats. I hadn't planned it that way, but training with a strong crew brings out the best/worst in me. I was getting stonger, I could still train, I when the session was over, I cold tell that there was something very wrong back there.
Anyhow- due to career demands, I changed my training around this spring to where I was training alone. Since I wasn't working with spotters, I ended up deadlifting much more often and squating lighter weights using no gear or modest gear. During this time, my back fixed itself- no chiro, no ART, no fancy exercises or rehab techniques- just high volume, moderate intensity training. In my case, I think all the "easy" deadlifting (2's and 3's in the 70-80% range) helped a lot in stretching the ligiments in by low back and hip area.
I remember hearing somewhere that most pains that people identify as low-back related have less to do with the spine and discs and much more to do with the tight muscles/tendons/ligiments in the hip joint. It appears that that was the case for both of us.