I have been running for years. I have had to take breaks, but no more than a few mo at a time. I started a job where I do a lot of lifting, and have noticed that when I shift my weight from one foot to another, I feel some popping in my lower back. Most of the time when I work out it doesn't hurt at all. I just started back running again after another 2 mo hiatus and have added a few things to my workout agenda, including a little weight training. I am sure some of this as exacerbated the problem.