I think the syllable "ㅎ" as in "않" is bothering you, but it is pronounced exactly as "안".
"않" itself is pronounced like "안", but it will make a difference when it comes to "않다".
As in "않다", the syllable "ㅎ" affects the next word "다", and makes it pronounced like "타(ta)".
let's see how it is pronounced
안다(i know sb or i know about sth) : /an da/
않다(make sentences negative) : /an ta/
안+ㅎ+다 = 안+타
it's just my two cents.