Why is my refrigerator making unusual noises?

Many sounds are normal for this refrigerator, including buzzing when the water valve fills the ice maker, pulsating from fans and the compressor adjusting performance, hissing or rattling from refrigerant flow or water lines, sizzling or gurgling during the defrost cycle, and popping from the expansion and contraction of inside walls. Creaking or cracking occurs as ice is ejected from the ice maker mold. (Page 10)