Well I've had this from deadlifting a few years ago.
I was dead lifting only around 225, but there was a loud pop, and my lower back immediately got stiff and painfull.
The pain didn't go away so I went to my chiropractor. He recommended ibuprofen, or aleve. Using a cold pack for about 15 to 20 mins 4 times a day. Also, laying on my back with neck support, on a hard flat surface for about 30 mins a day. (neck support can be a tightly rolled large bath towel underneath your neck)
My pain went away within days. It was caused by my joint that connects to my pelvic/hips in my lower back, causing the muscles to contract in order to overcompensate for the bad form from my dead lifts (I was an idiot, just starting my weight lifting, and didn't take enough time to focus on my form).
Hope this helps!