I'm getting the same 1 sec freezes too. Happens all the time, regardless of what I'm doing. Every 10 to 15 seconds I'll get the quick stutter, but it's very noticeable. 
  
I've tried everything possible on my side to try and fix this - reinstalled my OS, made sure all drivers are updated, disabled services connected with stutter problems, tested low, medium and high settings, installed a different 1.12.1 client, disabled sound to verify it wasn't a sound driver issue, and scoured the internet looking for solutions and trying all that I have found. Still the same result. 
  
I've played on several wow servers from vanilla to wotlk and this is the first time I've ever encountered this so I have to agree with what's been said so far, it has to be a server side issue.