I had that too on my MC. Not all the time....but enough to bug me! Are you drinking lots of water in between your lemonades?? I drank about 2 and a half litres of warm water daily and that certainly helps. But the quick fix is to stir up 1 tsp of baking soda in 1/3 cup of water and slam back. Stay sitting up and then you'll burp like crazy (so you gotta be alone when you do it - then it's fun! ha.)...and, voila, the heartburn goes away. The soda alkalizes the system. The maple syrup is acid-forming....
I hope that does it for you!