If WQAchievements is enabled there's a hitch that grows over a session when an inventory item is added to your inventory. The easiest way to see it is to mail a bunch of items from a different character, open the mailbox and hold down a turn key so you're spinning in place. As you take each item out of your mailbox there's a hitch that is only present when WQAAchievements is loaded.

Weird. WQA does nothing with mail, looting and your bags.

Were you active before 8.3?
Does this happen if WQA is the only actice addon?

I'll take a look.

Couldn't reproduce