OOOOOH. Okay, but still. Villager sounds are funny (in my opinion) and zombie sounds are... well, regular zombie sounds.
I guess Spider sounds are somewhat weird (not necessarily annoying, but weird is a valid way to describe it), but other than that I can't really think of a mob that makes annoying sounds.
Maybe Phantoms? Although that as well is more creepy than annoying.
Or maybe Pillagers, because though I really like the mob itself, the sounds they make sound kinda strange to me. Too low. Too slow. Too much "A" and "R" in it. It sounds like "harrr", but in slow-motion.
It kinda makes them sound like pirates (which is not that surprising, because the early concept design of Pillagers did look like a pirate... and I'm VERY glad they changed that) I mean, I do like the sounds of (especially) Vindicators and (also) Evokers better.
Well, Creeper sounds are pretty annoying too, because when you hear it, you know you're SCREWED. However, I don't think that's what you meant.
Nah... Eventually, I don't think there's a mob from whom I really don't like the sounds.
Pffft. Why do I write SO MUCH when I'm discussing about MINECRAFT MOB SOUNDS? Hahahahaha!