Shower drain odor

I've recently noticed a sewage type of smell coming out of the shower drain in the master bedroom of our house. It only seems to happen about 30 seconds after I shut the water off though, and only in this one bathroom. There is another bathroom on the other side of the wall and it doesn't have this problem. No smell comes out of any of the sinks in the house or the basement. Just this one bathroom. I picked up some drain cleaner from home depot thats supposed to get rid of any grease or clogged hair in the drain but haven't used it yet. should I? any ideas what else could be causing this? I've read that it possibly could be an issue with the trap? We just bought the house 2 months ago so not sure if its been a problem in the past. Thanks in advance for the help

Take a flashlight and see if you can see standing water below the drain grate. A properly installed shower should have the trap right below the drain. They may have taken a shortcut and put only one trap for both of the showers if they abut each other. If so, you have a long trap arm that has accumulated crud in it.

Another possibilty is an improperly vented trap that gest siphoned dry, but that isn't as likely if it happens just when finishing the shower. I guess if you have multiple showerheads and a really big flow, just the volume could make it continue and empty the trap, but that is just a guess.

Tell us where the trap is. If you can take the screen off the drain, you can try scrubbing the pipe above the trap. If there's a bunch of crud there, that should solve it.

I tried looking down the shower drain, but can't see anything because the drain pipe comes up at an angle. Also haven't been able to locate the trap yet. The pipe in the basement only goes straight up and down. Could it be behind the duct? I'm pretty new to plumbing

It should be a straight drop to the p-trap from the drain in the shower. Now, if it doesn't have one, I'm surprised it doesn't smell more, but the flow of the drain water will rile things up a little. If the trap is a long ways from the drain, then that whole pipe is ripe for smells from accumulated body oils, soap scum, trapped hair, etc. A proper drain's trap keeps the vertical drop fairly small, and the trapped water keeps sewer smells out of the house.

Try putting a "dip stick" into the drain, and see if it comes up wet

that'll tell you whether the trap is really there, but just out of sight, not directly underneath the drain cover. Do the same at the other drain on the other side of the wall. There has to be traps. Find them first. Then, figure out how the drain plumbing is routed so you can describe it to others. There are traps, Vents, Wye's, Tee's.

What size is the pipe in the basement?

David