Sorry to to not get back sooner. The 6000 and the 5800 btu units when first started and superheat is high will make (the best I can describe) a low duck decoy sound. A cross between a duck call and a sheep bleating, except lower frequency and somewhat muted. I have a 1981 GE top mount refrigerator with a static condenser. I use this only as an overflow unit now. Anytime the refrigerator is started warm, after a while the evaporator(frost free unit) will make the same sound as the larger BTU Carry Cools. The only thing that I can think of is that this is refrigerant gas flashing at the end of the cap tube going into the evaporator, until the evaporator is fully active and the superheat has come down.
I have a 1969 GE Fashionette that has copper evaporator tubing with the aluminum spine fin wrap. This unit always seems to run a high head and somewhat high superheat even after I recovered the charge, evacuated to around 200 microns, and recharged with virgin R-22. Even replacing the cap tube did nothing to lower the superheat.
I also have a 1989 GE Carry Cool that is one the higher efficiency 4000 something BTU units with the condenser off of the 5000 BTU units. This one has the Fedders Rotorex rotary compressor in it. The unit cools fine, but has a somewhat higher evaporator discharge air due to the smaller compressor and larger evaporator fan and condenser coil. The compressor has a bad discharge check valve on it and when the compressor shuts off, it will back spin the compressor till the pressures have equalized. Makes a heck of a clatter.
Hope this helps.