Smells within a bathroom are obviously never welcome. Water infiltration in a tiled shower is often noted when the tiles are able to move. If you try to shift each tile on the wall and there is no "give", it would seem unlikely that water is getting behind the tile. If moveable, the shower water has found a way beyond the grout and will eventually the green board/cement board/etc behind the tiles will mold/rot. Another easy check method would be to go to the floor below and look/smell for moisture. Unfortunately with many shower leaks the first thing to notice the water infiltration is in the ceiling below the shower. You may want to revisit the types of products used in the rehab project a few years back as simple drywall was the wrong product for the humid conditions of a shower wall.