It happens about 5 minutes into most phone calls on iOS11 using my AirPods. Very frustrating (I talk around 3000-4000 minutes per month). Only happens for 2 seconds and then corrects itself but the "slow-motion / hand on a turntable" description is exactly what's happening. The Apple Store said they tried it and nothing happened so it must be a carrier issue (Vodafone NZ).
Same thing here. I'm on iOS 11.3.
What I hear slows down - the "hand on the turntable" description is perfect. I've been told a few times that the other person says my voice is very fast, like a chipmunk.
It's like the data connection between the bluetooth and iPhone stops for a few seconds, and then catches up to real time.
It's not a carrier issue - switching to speaker phone resolves it instantly every time. And it NEVER happens on speakerphone while it is now happening on every call with the AirPods in.
I'd be interested to know how many people have the issue and what, if anything, can be done to fix it!