I removed the rear panel to determine the issue and found ice had accumulated around the fan resulting in the fan blades hitting the ice jam and creating the noise. The fridge was going through defrost but not consistently to melt all the ice. I replaced both the defrost thermostat and temp sensor to fix the issue, so far so good. ApplianceProParts has always taken care of my needs with having the parts in stock with fast shipping, always 5 stars!