I believe t turning into a d sound occurs more frequently with th than t.
For the word "the", the th is changed to a d sound // which is slightly different than /d/.
The occurrence of a t changing into a d sound occurs more frequently at the end of the past tense of some words like "spiked".
Perhaps it would help if you gave an example of a word you are thinking about where t changes to a d sound.
Student or Learner