Change in pitch of exhaust accompanied by some feelings of vibrations in the cab while driving.

Went to start my car up last night and after driving a half mile down the road, I noticed that the exhaust sounded much deeper and you could feel some vibrations in the cabin when giving the engine some gas. Not something that shook me out of my seat but enough to be worried about. I had a friend who was more familiar with cars come look at it, and said he heard rattling from the exhaust but he wasn't sure if it was something like a blown gasket in the exhaust itself or something with the engine causing it. Any ideas what the problem might be? Would it still be safe to drive ?