Ever since about 1.4, NPCs in Skyrim all seem to have the hiccups. Speech sounds will drop out once in a while, very briefly, but very annoyingly.

Instead of, "We send you to plant some phony evidence, and tip off the town guard," Vex says, "We send you to plant [silence] and tip off the town guard." Stuff like that.

It doesn't happen the same way every time for a given line. The general speech system just drops out for a second at random in the middle of any conversation.

Any help?

I've noticed that a few times, too - generally when I've walked past an NPC who was giving their usual spiel though. So plenty of 'I used to be an...arrow in the knee' lol
No idea what's causing it though, and I only noticed it since 1.5.

Yeah, it might be a 1.5 thing. Not sure when it started exactly.

It's 1.4. That's when it started for me. Reminds me of that one patch for New Vegas, that had exterior sounds (wind, distant gunfire) playing while down in a vault.