the noise is at all ventlevels, a/c, defrost
have a knocking noise under my dash in my heating/ventilation when I turn it on on 2005 Pontiac Sunfire
Dose the noise go away after the mode has changed or does it continue all the time? Do all of the modes work normally and it the heat and cold settings as they should be? Can you make it do it any time? You may need to bring it by the shop so we can hear what it wounds like. I am suspecting a broken mode door or something like that.
It continues all the time on all modes. The modes all work, however with the knockng noise. It did it at one point last winter then quit. It started doing again last week with the recent cold spell
It has to be a broken part in the heater and the only way to find out is to diagnose it which will probably require taking it apart to find what is broken. Give us a call if you would like us to do this work.