I have be paying attention to when I feel palpitations. I am noticing an increase or onset of palpitations when my stomach is growling, full, bloated, in pain, or gassy.
I notice them more when my stomach has gas bubbles and I can feel the pressure. Or I'll have a palpitation and right after or shortly after I'll belch.
I suspect it's irration of the 10th crannial nerve (the vagus nerve) since that nerve controls some of the more important aspects of bodily function including the heart and the stomach. But I'm not sure if others have noticed!