The metal in some anode rods can react with some water to produce that smell. The choice is to either remove the anode rod as suggested, or to replace it with one that won't react to the crud in your water. To get it out, you may need an impact wrench, since they are in there tight, and it's been there awhile. the anode rod is more technically called a sacrificial anode, and it is the 'weakest' thing in the tank, and gets eaten up first, rather than the tank rusting out. So, removing it can speed up the demise of the tank.