In the Skyrim Mods subreddit, there was a pretty hefty thread about the downgraded audio quality of Skyrim: Special Edition. Evidently, Bethesda has compressed the audio beyond reason, and people are noticing.
Thankfully, part of the development team responded and said that they are working on a fix and hope to release it by next week.
If you don't want to wait until then, visit the thread linked above. Being a mod community, it should come as no surprise that many of the contributors have already found work-arounds. If you're on Xbox, perhaps the mod will be available there as well.