Громкую is pronounced with an "oo-yoo" sound at the end - see here. I don't think that the яя has a yaya sound - see here or here. Instead, I regard it more as a "yuh-yuh" sound - see rules for vowel reduction here, which indicates that after the stress, the я takes what that page describes in section 6.3 as a "yuh" sound, or an apostrophized schwa. (I may have made up the word "apostrophized." Sorry.) Since both я's are after the stressed vowel, they are both reduced.
I do not think the Duolingo audio is fantastic on pronouncing this particular instance of громкую.
I don't know if it's relevant to Russian, but there's a difference between "not like" and "dislike". I can not like something by being indifferent to it - I don't know about something, so I don't like it and I don't dislike it. If I dislike something, it means I have a definite negative opinion about something. The two things are not the same, although people often use the two verbs as synonyms.
Mainly, "любит" means "he/she loves" only when the object is a person; otherwise (as here) it means "he/she likes." https://www.duolingo.com/skill/ru/Infinitive%2C-Likes-and-Dislikes
I'm not sure about "Mum." Here's the course policy: https://www.duolingo.com/skill/ru/Basics-1 "Just to make it clear, we are using American English in this course—but don't worry, we will accept all versions of English where appropriate. Just be careful around expressions like 'bathroom' or '1st floor', because these may mean different things than what you are used to." (Dinner/supper is a big one.)
My friend, try this site - it will help you see the patterns of the endings: http://www.russianlessons.net/grammar/adjectives.php
I always also recommend this site: en.OpenRussian.org - since it is an online, searchable dictionary that has (just about every) adjective you can think of, as well as all the declensions.
опять какая то самодеятельность составителей курса,
love - любит
like - нравится
My mom does not like loud music - моей маме не нравится громкая музыка.
My mom does not love loud music - моя мама не любит громкую музыку.
love и like можно использовать по отношению к чему угодно, необязательно к одушевленным или неодушевленным предметам, по сути это синонимы
In this same course: я не люблю громкая музыка and мне не нравится громкая музыка. Considering they relate to a same kind of situation, according to my understanding, the second should be right here. Or shall one consider that they dislike "continuously" loud music and that thus, the first one is correct?