knocking behind dash

[Mark109]

T 800 09 turn the key on there is a knocking behind the dash . Goes away in 10 sec . I have been told that it is my HVAC actuator , but I unplugged it and turned the key on and the knocking sound is still there . Is there 2 actuators on them . Or any other ideas. Thanks

 

[Duck]

I know a guy who had to have reinforcement plates TIG welded onto his firewall to stop it from cracking. It was a shit spreader 9400 with a bazillion miles on it. But that's what the symptoms were.