Yes, it adds air (oxygen) to the exhaust to boost catalytic converter operation until oxygen sensor heats up and controls the fuel mixture for correct oxygen balance.

This only happens initially after starting the engine, and it does have some noise during that time.

Of course, I can't hear wether your noise is usual or not.

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1991 300SEL (W140)
1987 190E 2.3 (W201)
1987 Honda Accord 2.0