Is there some specific explanation to the "throbbing noise" that some window compressors produce?
In my quest for a "quieter" window-shaker I have recently purchased a wide/short 6000 BTU top-exhaust Sears/Kenmore model 75062 for $250:
The indoor fan itself is definitely much more quiet than most generic window air conditioners that use a shared indoor/outdoor axial fan motor, due to it using a separate long skinny small-diameter squirrel cage that is some two feet long, spanning the width of the front of the unit. At the lowest fan speed the indoor fan is very quiet but still moves a large amount of indoor air..
However the compressor is another story. It is quite loud, and makes a "throbbing noise" when running. Clearly the compressor has a loud 60 Hz vibration simply due to powerline frequency. However, it is not at all obvious where the approximately 0.75 sec "throb-throb-throb" noise comes from. The whole window frame vibrates due to the compressor throbbing.
It is probably some combination of compressor resonant frequency and mounting rigidity, and the fact that it is most likely a wobbly scroll compressor. I wish the compressor were quieter but there probably isn't anything I can do about it.
I would probably be much happier with a 2-stage compressor system, with two separate high/low power compressors, though since window shakers don't usually go into this level of technical complexity I do not know where I can find a small window A/C that contains two separate 350 watt AND 150 watt compressors capable of operating in parallel on the same cooling circuit.
I don't own this building so there is no way I can install central air with an outside compressor. Wish I could, but it isn't going to happen.