[tkw]

GE top-freezer model TBX16SIBSLWW has started making a new noise that
it wasn't making before. Each time a cooling cycle begins, a knocking
sound can be heard coming from the freezer compartment approximately 15-20
seconds after the compressor starts. The knocking lasts 10 seconds, then stops.
The rest of the cooling cycle is OK--just the normal compressor sound.

Problem is not with the compressor because:
1. I've localized the sound by moving my ear against the back of the fridge
to about 4 inches above the bottom of the freezer door level.
2. The compressor starts normally and sounds normally for 15-20 seconds.

Problem is not with the evaporator fan because if it were it would happen
whenever the fan is spinning, not just for 10 seconds on cycle start.
Bad fans are bad continuously or maybe randomly noisy, but not in such
a periodic pattern.

I've disassembled the freezer to reveal the evaporator coil and placed some
fiberglass insulation between the coil and the plastic cover with no effect.
(Didn't fix it.)

Problem is difficult to isolate because if freezer door is opened and cover
removed knocking stops (i.e., trying to debug it in that way won't work.)
Problem also doesn't happen when fridge is started the first time after being
off for a long time. It seems to happen only when the fridge is in steady state.

This fridge has no mechanical damper, just a plastic gate to set the freezer
temperature relative to the lower compartment and a single knob in the
lower compartment. Making the temperature cooler calms the knocking a
little, but doesn't solve the problem. Also, I don't want my milk frozen! :-)

Functionally, unit is perfect.

Only suggestion I've heard that matches all the evidence is that the knocking
occurs when the freon enters the evaporator initially because the cooling
cycle is just starting and the metal starts expanding or contracting. (I.e.,
starting the cooling cycle jars the system out of steady state.) As the
evaporator adjusts to the freon flow it stops knocking. However, the question
is why this noise just started, if it's a natural part of the design.

Does it mean I'm low on freon? The unit still works perfectly.

Sound is driving me nuts.

[kayakcrzy]

I cannot find your model #. If it has a motherboard, it could very well be your problem. If you pull the refrigerator out, and look in the back, if it has a motherboard, you will see a panel with three screws holding it in, and that is where it would be. Take the cover off, and see if that is where the noise is coming from. If you need me you can reach me at my web site at ApplianceEducator.com Tom

[Icehouse]

Sounds to me like the motor is wearing out. These are what is known as "skelaton" type motors. What you are hearing is the rotor moving back and forth in the stator a condition that happens with age in these motors. It stops once up to speed.