I have a 2003 silverado ext. cab 4x4 2500HD 6.0. It has dual manual climate controls. I know these are known to have some problems inside the dash. My first problem was only 2 out of 5 blower speeds working for heat/air conditioning. I replaced the blower motor resistor and that fixed it. My second problem I am having troubles with is when I have the A/C on, every once in a while (anywhere from 5 second to 20 second intervals), there is what sounds like a big release of air pressure. It only lasts for 1 second, but it is extremely loud. I can tell it's coming from under the hood, not inside the cab. When it happens, there is a minor loss in power of the motor, my head bumps forward while going down the road every time I hear it. As soon as I turn the air/heat off, I don't hear it anymore.

Most forums I read suggest to replace the blend door actuator but nothing really fits my description. I don't think my blend door is faulty because whether I have it on defrost, feet, face, or a combination of the 2, it works as it should.

Any input would be appreciated,
Thank you
Alex