Yeah, Duolingo will mess with you in this respect... I've heard a few polyglots recommend the site forvo.com for the purposes of pronunciation, although I don't really use it. Well, after I've learned English I tend to stick to languages with more or less strict phonetic spelling (which isn't actually one of my rules... but I suspect it helps me keep my sanity anyway). So I learn the pronunciation rules once and mostly don't have to worry about it anymore... Although on second thought, German is a language that benefits from double-checking, due to, well, compound words among other things.