I also have a similar issue, though it's not all sounds, just the dynamic stuff - weapon firing sound effects, NPC smacktalk, explosions etc. Sort of like fighting Alvin & The Chipmunks LOL
Audio set pieces like mission result chatter e.g. "We'll send X person to escort the civvies to safety, well done Agent" isn't sped up
Happened after a few hours of gameplay, after the most recent patch.
Started noticing audio glitches about 2 hours before things sped up. Most noticeably interior sounds became muffled and muted, and music became overpowering. Moving outside structures into the street again, it was all good.
Outside of game normal Windows sounds were fine from VLC player, also in other games like AC Oddyssey, and Division 1
Using Sennheiser PC363-D on USB interface if that helps