Dave wrote:
I had a smell in one of my bathrooms. It was a bath room I hardly used. What
I discovered was that the water in the sink and shower traps had dried out,
so from then on I run water occasionally in each to fill up the traps, now I
don't have that problem anymore. Could that be your problem too?

I've had the same experience. Absolutely nothing wrong with sewer line,
no slowing or backup. Just have to remember to run some water in the
guest bath now and then.