A murmor is "more or less" defined as any sound abnormal to a regular, healthy heart rhythm.
I've always had doctors tell me I have a murmor because of a baffle and shunt that passes blood around in the right directions from my first OHS which was done after i was born to correct a congenital heart defect. Doctors that don't recognize this start asking all kinds of questions wanting to be sure that I know it's there and that it's SUPPOSED to be there.
Now I click too, but I haven't seen a doctor yet who didn't recognize that for what it really was.
I'll note that many children often have what's called "innocent" heart murmors which just go away in time. There's nothing really wrong, just that small hearts tend to make some funky sounds. My son had one when he had a fever about 2 years ago. He's quite heart healthy.