I have a sewer smell coming from my upstairs (3rd floor) shower drain. The bathroom shower on the other side of the wall has no smell. The vent stack is not obstructed on the roof.

I had a tile guy come in and say that he needed to rip up the entire tile floor and then have a plumber replace the water trap and possible the drain pipe. I'm wondering if I can just have the plumber come in and replace it while only tearing up a few of the surrounding tiles around the drain pipe? Or does it all need to be ripped up so the plumber can better see what the problem is?

Also, it's a 70-year-old house. The tile guy said that the shower floor is three inches higher than it used to be before it was remodeled years ago (before I bought the house). He said there might be a gap between the tile and the drip pan (or maybe he said below the drip pan) where mold is forming causing the smell. But it sure smells like sewer gas. And if it was a water leak wouldn't the ceiling below be showing water damage by now?

I'm wondering if maybe the original shower floor was a solid (steel?) one with NO tiles. And when it was remodeled, the previous owners wanted tile so they had to then install a drip pan and tiles on top of that, thus causing the floor to be three inches higher than it previously was.

Any thoughts?