Last night I heard a gurgling noise coming from the toilet. Later when I lifted the lid I saw that all the water had emptied from the bowl.There looked like a powdery residue at the bottom, and there was powdery stains on the underside of the lid.I flushed and it filled up with water again. It hasn't happened again over the last 24 hours. Is this a sign something has gone wrong with the toilet itself. The toilet is just over 2 years old.