I have noticed with certain words that the sounds run together, at least according to the audios...for example, "uma maca" (I don't have the accents on my keyboard) always sounds like mah-muh-suh...and "eu nao tenho um cavalo" always sounds likes eu no ten-uhm cavalo...are there certain rules for this?
if you don't have the accents, why don't you just look for the keyboard combinations? http://symbolcodes.tlt.psu.edu/bylanguage/portuguese.html
Try Bing or Google Translate. Copy the sentence there and listen to the (differences in) pronunciation. That gives you another tack, and you can also spot when DuoLingo is wrong. Which happens. Of course, you cannot do this in the "listening exercises," but you get the idea.
The pronunciation is a problem, because if you want to speak portuguese rather than just read it, you don't know whether to mimic the robot or not. There could soon be an army of duolinguists out there speaking Portuguese that can only be understood by other duolinguists. Or robots.