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thats a weird thing, My guess would be its a dead mouas or something that got into the refrigerator somehwere underneath and is dead and when the fan underneath comes on you smell it. I would call right way and have the refrigerator either looked at or replaced. I would personaly have the refrigerator replace because they will either tell you they dont smell anything or wont be able to find the problem. my guess like I said is a small animal died somewhere under this.