Our home was built in 1995. We replaced the original faucets and countertop a year ago. Now we get a sewer smell from one of the sinks any time we turn the water on. It does not do it every time. We have tried cleaning the pipe via rooter. The city water department says the trap is burping. Only one sink does it and the other is only 4 feet away. Any idea what the problem might be? Trap, etc., are all the same as before. We also cleaned the overflow drain.
When anything organic breaks down in the absence of oxygen (which is sometimes the case inside drains) it smells to high heavens courtesy of biogas - the gases produced from the breakdown.
This is not an uncommon problem, and there's one way to find out if this is what you're dealing with: Disassemble the drain completely in the sink producing the odor and clean it thoroughly with bleach and water solution. If there's an overflow in this sink, make sure to run the bleach solution through that channel, as well. Reassemble, and note whether the smell fades over the next few days. Good luck!