How do Americans pronounce the letter "t" in the end of words? Do they pronounce it like a "d"?
A "T" on the end of a word may be pronounced "D" if the following word begins with certain sounds and the words are being pronounced rapidly. Peter Shor's example of "I put it back" is a good one.
Basically, if "put" is not for some reason being emphasized (as when your mother tells you "PUT ... IT ... BACK!!"), then the "T" sound in "put" is abbreviated -- the percussive "T" ending sound due to the tongue completely stopping air air flow does not occur because the mouth is already preparing to pronounce "it".
This is just normal speech, and is unlikely to vary much by dialect.