Is it normal for my Whirlpool refrigerator to make unusual noises?

Yes, several noises are normal for this refrigerator. These include buzzing when the water valve opens to fill the ice maker, pulsating from fans and the compressor adjusting performance, hissing or rattling from refrigerant flow or water lines, sizzling or gurgling from water dripping on the heater during the defrost cycle, and popping from the contraction and expansion of inside walls during initial cool-down. (Page 10)