You aren't making sense. The fact that Billy Graham said some believers believe the rapture is 'secret' means that the idea of 'secret' is not inherent in the word 'rapture', or else the word 'secret' would not need to be used.
'Rapture' refers to the catching up of the saints referred to in I Thessalonians 4. Pre-trib rapture folks will debate the pre-trib versus post-trib rapture. So 'rapture' does not refer specifically to post trib.
Post-mils historically used the word 'rapture' to refer to the catching up in I Thessalonians 4. That is how pre-tribbers use it. If you say you do not believe in the rapture, you are saying you do not believe in the saints being caught up to meet the Lord in the air. You can say you mean something different, but don't expect listeners to understand you, especially if you are talking to pre-tribbers.
It's kind of like calling Muslims 'evangelicals' because they share some of the same voting concerns in the US electorate.
See, 'rapture' used across exchatalogical lines.
I sat under dispensationalist deceit for years and they do indeed teach a "secret" rapture that leaves the lost scratching their heads at what on earth happenedf? Martians come and abduct those missing people?? All your claims to the contrary, you do NOT find a secret rapture in commentaries before dispensationalism. The dispensationalists use the trick Communists and other tyrants use: slyly give new defintions to words to fool the simple. If you cannot tell the difference between how the Billy Graham organization explained "rapture" as used in the evangelcal world today, largely dispensational; and how the word rapture was used before dispensationalism, there is no help for you. You do not find the rapture connected to the "great tribulation" which commences after their secret rapture. The scriptures themselves refute the idea of it being secret:
"For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:" (1Thess 4:16, KJV)