Q: My Sentra makes a Knocking sound when I Accelerate or Brake

You probably have one or more motor mounts failing. The motor mounts have a rubber buffer in them to soak up the engine vibrations and when they get tired the engine can shift around a little bit. The one that is most likely causing your noise is called the "Reaction Rod" and it is a support to prevent the engine from twisting in one direction or the other when you put a load on it. Your motor isn’t going to fall out, but since it is moving around more than it should, it may damage some other components. You can get this fixed conveniently by contacting Your Mechanic. They can send a technician to your home or office to check out your motor mounts and tell you which ones need changing.