Product review (4 stars): Don't be scared, it is the Bottom plate!
I've read about that loud hammering sound here a lot. Unfortunately, just today, two days after I tried mine. I had the same problem and I was almost scared! It is the bottom plate!. Install it with concave side facing to the floor! Manual is useless telling it which side! Also, make sure to use some faucet wrench to install that faucet adapter, otherwise you'll definitely get wet! Aslo, keep the hoses up after you're done since it still have water in them. After this horrifying start, now mine works well.