I only hear it if I lay in bed a certain way with one ear pressed against the pillow, and that's been true since childhood so has nothing to do with afib. I think it's pretty common to be able to hear heartbeats. That's particularly true if you have hypertension. Had your BP checked lately?
Obsessing on minding your heart beat is never good. People do that with their Kardia and Apple Watches and such, and all it does is raise their stress levels even higher. I would try to shift attention to something else whenever you find yourself paying attention to it. Play some music or something to distract yourself from it.