I am on my second brand new unit of this AIO and have had the exact same issue. A persistent loud buzzing noise almost like a chainsaw. When I tap the cooler it stops momentarily.
My first unit went a month before it started making this sound, this one lasted a day. Does anyone know what the cause of this is and how to remedy it? I really would prefer not dismantling my system again and getting another replacement.
Here's a link to the Reddit thread I started when the first unit went