For anyone looking to pronounce "Ramadan" with the original Quranic sound "d", this paper has a hint.

It is a lateral consonant, so when pronounce it, you must get air to flow along the sides of your tongue. Like English "L".  

#RamadanMubarak https://www.academia.edu/3745721/New_Data_on_the_Delateralization_of_Dad_and_Za

The Quranic "d" sound, represented by the letter "daad", is possibly unique to Quranic Arabic. So much so that early Arab scholars often called their Arabic "the language of the dad".

The sound does not exist in modern Arabic anymore.