The air pump probably has a diverter valve that dumps the
air into the engine compartment until the engine is up to
temp so that the catalyst will work. This unmuffled air
will have a high pitched sound due to the vane pump.
The alternator will be charging heavily the first few
minutes after starting, and will make more whine than usual.
And the power steering pump will make more noise than usual
with cold, thick fluid.
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