My cobalt 2007 makes a knocking noise in the passenger dash when I turn on the car what can this be?
Is that where the hearer coil is? You may have air in the system. Without hearing the noise or if it is doing it before start up or after heat up? Are you sure it is in the dash or under the hood? It may be a belt becoming frayed and part of it is hitting a cover guard. Have the engine checked while the motor is running.
Recirculation air flap under glove box, caused by cheap foreign parts that go out. Flapper is shot. Big issue in cobalts
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