Since your comments and question appear to be addressed to me, I will answer them.
Offenbar ist die Frage nicht ganz einfach, wenn mehrere Muttersprachler verschiedene Aussagen machen - I believe you are mistaken about that. The issue is, to my mind, quite clear. Britons generally say adult while Americans generally say adult. Some of the posters above are British or have learned British English, others are from North America. Check the profiles of the various posters and this will become apparent to you. So there is no difference of opinion in the sense that posters are disagreeing with each other. They are simply pointing out a difference in pronunciation between English as spoken by North Americans and English as spoken by Britons.
yTurp's claim in #8 that the pronunciation of "adult" depends on whether the word is used as a noun or an adjective is absolute and utter nonsense. Not only that, it is quite typical of the sort of thing that yTurp posts here. His/her suggestions are, in most cases, outlandishly wrong, as many others have also observed.
You may find my comment harsh. I assume that's because you are not familiar with yTurp's erroneous and, in my opinion, deliberately, misleading offerings. I would prefer the LEO database to contain as much reliable data as possible and not yTurp's garbage.
Who, by the way, are all these people who are feeling abgeschreckt?
Sadly, yTurp is not among them. You may want to consider why that is.