It appears to me that ㅎ isn’t always pronounced the same way, and that it sometimes – apparently only word-initially – is pronounced almost labially. (Note the quotation marks in the title.) I first noticed this in Blackpink’s hit ‘휘파람’; but note in this song the difference between 1′36″ and 2′48″ (YouTube links). At 1′36″ it sounds as though they are pronouncing it the same way we do in Western European languages (English, German, Norwegian, etc.), i.e. glottaly; whereas at 2′48″, it definitively sounds as though it is pronounced semi-labially, i.e. by blowing through slightly pursed lips.
I have noticed the same thing on Duolingo. In a word such as 환영합니다, it sounds as the first ㅎ is semi-labial (though not quite as pronounced as with Blackpink), whilst the latter is glottal. Is my observation correct? And if so, what are the pronunciation rules governing this? Might it just be that this is a dialectical thing? I have not seen this discussed in any of my learning material and cannot find anything when googling for it.
P. S.: Any edits providing better tags is much appreciated.