It would be rare to find a noun just sitting by itself in a sentence. Rather, in Korean, one of many particles (or other things) would be attached to it.
For example:
닭과
닭만
닭이랑
닭이다
닭이나
etc…
If the thing that attaches to these words starts with a consonant, the same rule from above applies, and only one of the two bottom consonants is pronounced.
닭과 – 닭만
(This sounds closer to “닥과 – 닥만”)
However, if the thing that attaches to these words starts with a vowel, the pronunciation of the final consonant, in theory, should move to the upcoming syllable. For example:
닭을 – 닭이다
(This should sound closer to “달글 – 달기다”… but I admit it does sound like 닥을 – 닥이다.)
닭 is a noun, but various things are also attached to verbs/adjectives as well that change pronunciation.
The following are three common verbs in Korean that have this fourth letter (All verbs end with “~다” but don’t worry about that for now):
앉다 = to sit
읽다 = to read
없다 = to not have
Listen to the pronunciation of each of those words. You will notice that (just like the word “닭” above), because each of the four-letter syllables is followed by a consonant (다), only one of the two final consonants is pronounced. As you can here, the letter that is not pronounced is not the same is ever word.
In 앉다, ㅈ is not pronounced (sounds like “안”)
In 읽다, ㄹ is not pronounced (sounds like “익”)
In 없다, ㅅ is not pronounced (sounds like “업”)
If the thing that replaces “다” starts with a consonant, the same rule from above (with nouns) applies, and only one of the two bottom consonants is pronounced. For example, if 앉 is followed by a consonant:
앉겠다 – 앉고
(This sounds closer to “안겠다 – 안고”)
However, if the thing that replaces “다” starts with a vowel, the pronunciation of the final consonant moves to the upcoming syllable. For example, if 앉 is followed by a vowel:
앉아 – 앉으면
(This sounds closer to “안자 – 안즈면”)
You can see the same phenomenon with all words that have this 4th letter. Let’s listen to “읽다” when “다” is replaced by something starting with a consonant compared to a vowel.
Followed by a consonant:
읽겠다 – 읽고
(Sounds closer to “익겠다 – 익고”)
Followed by a vowel:
읽어 – 읽으면
(Sounds closer to “일거 – 일그면”)
Let’s do the same thing with 긁다 (to scratch)
Followed by a consonant
긁겠다 – 긁고
(Sounds closer to “극겠다 – 극고”)
Followed by a vowel
긁어 – 긁으면
(Sounds closer to “글거 – 글그면”)
I used this link to answer your question. Read the whole page for more examples.