So I noticed my refrigerator seemed to make a knocking or hammering noise when a toilet on the other side of the house was flushed. I have a Whirpool side by side refrigerator and Toto toilet. The refrigerator also occasionally makes the noise without flushing the toilet. After scouring the web it sounded like a bad refill valve in the toilet causing a water hammer. I replaced the valve in the toilet and that appears to have fixed it. The toilet itself had a very small knocking going on with the water line once the toilet was almost full but was barely noticeable. However, the noise on the refrigerator side was quite loud. I just wanted to post this in case anyone else ever experiences the same issue.