I'm doing the StrongLifts Advanced 5x5 workout (very similar to Madcow, SS, etc) where I squat 3 times a week. It has been BRUTAL on my low back. I think I'm doing something wrong in my squat or deadlift (or both), so I've posted vids for analysis.

I know I need to get this worked out or I'm going to hurt myself. I can feel it.

Deadlifts: http://www.youtube.com/watch?v=uGdU9pP3GCo
Squats: http://www.youtube.com/watch?v=jL7D64xD5ZQ

Note: in the squat video I'm (trying) to do LOW BAR squats, as that's what Rippetoe, Medhi at Stronglifts, and others recommend. I had been doing (up til now) high bar squats. I didn't even realize there were different ways to squat until very recently and was doing high bars by default. Rippetoe says in his squat videos on youtube that low bar is easier on the lower back, which was very counter-intuitive for me because it seems that the additional forward flexion of the back would ADD stress. But what do I know...