The discs in my backbone feel like they are grinding against each other. i have been doing the insanity workout for approx 2 weeks now during my lunch break. when i get home in the evening, my back is very stiff and i can feel the discs in my backbone rub

Starting : Starting to exercise is hard on the body especially when you were inactive. It sounds like the "insanity" workout is too stressful on your back. You would probably benefit from stopping "insanity" and then start with a beginner workout and slowly build up to "insanity". Last thing you want is to hurt your back. I would discuss your pain with your primary care doctor, physical therapist and trainer. Good luck!