Jay Chan said:

My another alterative is Delta CP200. According to the spec, it is
described as having a quiet motor.

Another point I forgot to mention is that it isn't the *motor* that
makes most of the noise - it is the compressor itself. The air pump
doing it's job of moving air around rapidly. The intake and exhausts
of the compressor pump are where most of the noise comes from.

It sounds like you are looking for a vibrating diaphragm pump. They
are generally quieter than a piston pump. You could operate one of
these in an apartment and no one would notice. The problem is, they
are slow to generate much air pressure.

FWIW,

Greg G.