Well I was sitting here at my computer, composing an email. There was a strange noise from the kitchen. Sounded like gurgling. Then there was a small pop and, when I went in there, and acrid smell. The fridge seems OK, but it is now where the noise was coming from. The dishwasher seems OK. the microwave was turned off. It works when turned on. Very strange stuff. The smell has gone now.
That’s be back-pressure on the sink’s plumbing forcing gas from the sewerage through the water-trap in the u-bend. Maybe someone in the building flushed a cherry bomb. 🙂