I too have had similar experiences. My doctor likewise has brushed it off. I have read where there is a connection, via the vagus nerve which can be stimulated and cause palpitations. Google it, you will find there is a lot of information about the connection. I was recently weaned off Metoprolol, and have experienced both palpitations and a fast heartbeat. However there seems to be a connection with eating. I have only gotten those symptoms, when I had eaten a large meal, and like you had to burp a lot. On days where I ate a salad for dinner, or a less filling meal, I had none.

Now I an on some ayurvedic medicines. Let me watch.

I have palp/irreg HR also associated with position, bending, belching, after eating and even after drinking.
Working in the health field as a Med/Surg Asst I went after answers. Asked for ECHO of heart, etc.
Heart physically fine. So......
Was told by chiro I have hernia. Hmmmm.
He pulled my diaphram down and it helped.

When they happen I do slow breathing.
Place ice pack on Left forearm. Recline with feet up.

I eat and drink slowly. Do not lift heavy objects.
Take EVERYTHING slow.
Very limited carbs. No sugar. No caffeine.
Gluten free.

I do have Metoprolol Tartrate 25 (take half if get prolonged irreg HR)

I rather do this than have hernia surgery.
It is a vagus issue for sure!

ALSO VERY GOOD INFO from Dr Sanjay Gupta/York Cardiology on Youtube. Great Videos on Afi/Palp