Is humming the Quran unconsciously, while changing or forgetting some verses during memorization, considered forbidden?

There is no sin upon one who makes a mistake or forgets in their recitation, because the sin of error and forgetfulness is lifted from a person. Allah Almighty said in the verse from Surat Al-Baqarah: "Our Lord, do not impose blame upon us if we forget or make a mistake." And Allah said: "I have done so." And He Almighty said in Surat Al-Ahzab: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended." It is recommended to strive for mastery in memorization and frequent revision.