Hi Faye,
Ketones are produced when the body is forced to burn fat rather than carbs to fuel itself. Therefore anyone, diabetic or not, could produce ketones when on a strict diet or even just overnight when they haven't eaten since the day before. These are often called 'starvation' ketones.
Ketones become problematic for diabetics who have too little (or no) insulin circulating in their bloodstreams. Under these circumstances the blood starts to turn acidic as the ketone levels (and usually blood glucose levels) rise. This leads to diabetic ketoacidosis (DKA) which is extremely dangerous and can kill within hours. As you are a Type 2, I would think that you are at very low risk of developing DKA. As the mum of two Type 1's, I'm not sure about Metformin, I think it sensitises your body to the insulin that your body is still producing, so should not really impact on your risk of DKA, but hopefully some knowledgeable Type 2 will be along to answer that question soon.
Your blood glucose rising will not in itself lead to ketones being produced, that will only happen if you have far too little insulin. I hope this helps.
Sue