Marshabookworm, yes been there. It's horrible isn't it.
Can you think back to any other times when you've had a run of these? And whether it was bang in the middle of your cycle? It might be that your body is struggling to ovulate as usual. I think mine were around this time in peri menopause. It always seemed to be when my body was doing it's best to ovulate and for me HRT (Evorel Sequi) calmed it all down.
I think it's a known thing that palpitations are more common in certain parts of the cycle.
I actually called a private cardiologist after having 2 day's worth of them, like pop corn popping in my chest. Thankfully they gave me an appointment for that evening and the cardiologist gave me a check over and said he wasn't worried at all. He did say the definitive check would be to have an echocardiogram, as if the heart is strong and structurally ok, it's usually considered benign. He said from listening to my chest he believed all would be ok and that it was ok to wait for an NHS appointment for that if I wanted. So I did. The test came back normal.
All the while my GP's were talking about anxiety

It was only when I came here and so many people here told me that they too suffered and that palpitations are a menopausal symptom that I asked my GP to consider HRT (I had other symptoms as well).
I'm not saying HRT is always the answer, I'm just saying that yes it can definitely be hormonal.
Sometimes having some extra salt on your food, and some magnesium and any foods containing taurine (meat mainly which I don't eat) can calm them down. Another thing the cardiologist said was if you notice it mainly at rest, that's very typical of a lot of healthy women, at rest is likely benign (but that doesn't mean it's not if it happens during exercise).
The GP's thought that you are too regular for it to be hormonal, I can see what they mean, but palpitations are known to occur at certain parts of a cycle anyway, and also I would query whether your oestrogen levels are low even though you are regular. I was regular but peri menopausal and hrt helped it so thinking it could still be hormonal.