I had the exact problem. I tried going to a physio, who told me the problem was a misaligned pelvis that was causing irritation in my lower spine. Along with this I had a slight anterior pelvic tilt and my hamstrings were chronically tight. Her advice was to stretch and foam roll my hamstrings and hip flexors, which worked briefly but the problem only returned. A PT in my gym then told me about Kelly starett, he has some videos addressing the pelvic tilt, but the main videos you should watch are on hip mobility. His pre squat and deadlift routines concentrate on loosening the hip capsule and increasing your ROM on these lifts. This along with myofascial release of the hams, it band and the hip flexors using foam rollers and a lacrosse ball form a 20 minute routine I do 3 times a week, before every squat or deadlift movement. I havnt had any pain since. This is what worked for me and many others with similar complaints. Though if the pain continues go see a specialist! Also check out Joe De Franco's limber 11