I am an experienced home service technician, and I recently completed a job to inspect a sewer smell coming from the upstairs area of a customer's home. The customer noticed the smell behind the shower and near the attic. I discussed the option of performing a smoke test to help locate the source of the odor, but the customer preferred to monitor the situation for now and track when the smell occurs. She mentioned that the odor was first noticed during a period of heavy rain. The customer will continue to observe the issue and keep us updated with any changes.