Regular zombie ambient sound is overlayed in zombie variant ambient sounds
The bug
There is a bug in which the idle sound of husks and zombie villager, and their baby variants, is overlaid with a regular zombie's version of the same sound.
How to reproduce
/playsound minecraft:entity.husk.ambient hostile @s /playsound minecraft:entity.zombie_villager.ambient hostile @s
It appears that say3.ogg is the only one affected out of the 3 possible ambient sounds, so this issue only occurs about 1/3 of the time. It does not affect drowned (only husks, zombie villagers and their baby versions).
See also: video posted in comments, showing this issue occurring with a baby zombie.