Ive read that some elders are able to say and hear the differences. In the tips and notes (pronouns?) explains some of that.
Also I've read that the newer trend to "ni" happens since past 50 years...which makes me wonder about regional dialects, especially comparing those closer to North Korea and China. Wondering if the differences can be heard in older audio or movies, especially if slowed down?
Does the pronoun sound similar to any of Chinese pronunciations? Yes.
I've noted and had to explain to some that "niga" or "nega" is a pronoun: It is not the insult in English that is used to mock blacks or other people of color. It's important to say here so people are prepared for cultural understanding.. From an elder Chinese lady, I learned to appreciate cultural contexts are equally important as definitions in dictionary or thesaurus.
(Duolingo design is to guide us through the language structure. I appreciate and enjoy the importance of Stories in the German and Spanish. One day in the future, I know this valuable tool of storytelling will happen in other language pairs like Korean.)
In olden times, 에 and 애 had slightly different sounds, but over time the two sounds were conflated into one.
If you are speaking "correct" Korean, the two words are supposed to sound pretty much the same. The sound change in normal spoken Korean is technically a colloquialism, and it's done only for clarity's sake.
(Also, on a side note, the programmers of the robotic voice obviously did not program a way for the robot to distinguish between the sound changes because it would be next to impossible.)