Chevrolet Repair: 2004 Chevy Silverado, chevy silverado, rear differential

Question
I own a 2004 Chevy Silverado, 8 Cylinders and it has 90,000 miles, I have noticed that when I am at a stop and when I release the brake I can feel as if someone has rear ended me.  Would you know what the problem could be?  Thanks for your time and hopefully you will have an answer for me.  Thanks again.  

Answer
one question. is it comming from the front, or rear of the vehicle. if its the rear, i would say start by checking your driveshaft and u joints if when you let off the brake and give it gas, it bangs, it could be wear in that area. if not you might have excessive play in your rear differential. if its the front, check your motor mounts for wear. start there and let me know how it goes.