Any possibility you're anemic?
It could be that as your body ramps up to digest certain things, it puts in a greater demand for oxygenated blood to your intestines. If you're anemic, that might cause a rise in your heart rate.
My pulse is steadily dropping since supplementing with liquid iron and using iron cookware. I haven't had palpitations either (but those are rare enough for me that could be insignificant)
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food