We live in an old home. A room addition was added upstairs w/bath and we have a sink, shower stall, and commode downstairs. The house is on a crawl space and the pipes converge right below the shower stall under the house on the ground level. We had a plumber snake the drain out to 100ft. And it was clear and everything running through, but it still makes a bubbling noise. What could it be? We did just have a snow storm and we have a roof vent, could this be the problem?

If the plumber snakesd 100 feet about the he snaked the sewer line and not the sink drain, Where did he snake from? You still have a partial blockage in the sinks drain line. Try snaking from the kitchen roo0f vent and seem if that doesn't help. Put out enough cable to reach the base and 15 feet more. Good luck, Tom