HI. Just so you know, Hissing and popping is normal on frost free refrigerators, it is the defrost heater, in this case. I would check these following areas to address any other abnormal noises.
If the level of the unit is not adjusted to proper specs, this will create an unstable operating condition, causing many noises to emit from the units structure. inspect the unit for proper level. adjust if needed. Next will be the drain pan. Once removed for cleaning, the pan must be replaced in position correctly. If not, the pan will rattle against the compressor, causing a ping or rattle.Simply reposition the tray if this is the case. The third possible issue will be the condenser fan. The condenser fan is located behind the refrigerator. It may be necessary to remove an access panel to reach it. This fan has a shroud, and if the fan blade becomes warped, it will rub against the shroud, causing noise. This fan blade is whole,and it can be removed and replaced if this is the case. Ok, the fourth problem spot will be the evaporator fan.
The evaporator fan is located at the back of the freezer. It may be necessary to remove obstructions such as the contents of the freezer, freezer shelves, ice maker and the rear inside panel of the freezer. The rear panel may be held in place by retainer clips or screws. Remove the screws or depress the retainer clips with a small screwdriver. Check the fan for warped blades. if the blades are warped or mis-aligned, replace it. This fan also is protected by a shroud as well, and it will make noise if the fan blade is damaged.
Last, i would move on to the compressor mounts. This is the most common spot for noise overtime. The compressor sits on rubber mountings. Those rubber mountings are designed to absorb vibration from the compressor. As the mountings age, they can become hard or disintegrate. When this happens, the compressor vibration is transmitted to the refrigerator structure and it can cause noise.
The compressor is located in the rear. It may be necessary to remove an access panel to get to the compressor.
Locate the compressor and remove the screw or retaining clip of just one of the compressor mounts.Using a pry bar, lift up the compressor enough to slip out the rubber mount. Inspect the mount for deterioration. The rubber should be firm but not rigid. If the mount is crumbling or hard, it should be replaced.
This concludes the inspection procedure. Follow carefully, and replace any failed or damaged device.