I have a 2000 Silverado 1500, ext cab., 4x4, auto., with 230k on it.

There is a strange knocking or tapping noise coming from the inside, front floor board passenger area (below the dash) when the heat is on, does anyone know what this is? The noise isn't constant, it comes and goes. My heat doesn't really work all that great either.

Thanks for all your time and help! .

 

probably air diverter doors.

 

Thanks! Do you know how to fix it? Are they easy to get too? Thanks again!

 

Remove kick panels on passengers side and hunt down the actuators: one for temperature , and two for changing vent locations. They can be tricky to get to. Then just play with the controls and observe what happens.

 

You can remove the glove compartment and get a better look and use a mechanic's stethoscope to help pin point the noise source.