Oh, it is not the first time I am doing this, I have built a few back in the good old days, including one from a (very!) old Soviet fridge. 50 years old and the compressor was good as new!
Main reason, it has to be very quiet. You don't get much better than a fridge compressor for this.
Unless you want to fork out about 200-400 quid for a Clarke Shhh! range... And guess what they use as a pump? Something that looks suspiciously like a fridge compressor! lol