noise under acceleration

Additionally, Rich, it’s ironic that we had the IAC, then the hiss, now the clicking. There are indeed vacuum lines that feed the blend doors, the actuators for operating the ducting for the HVAC There is a positive source of Vacuum there, and it initiates the opening and closing of these ducts.
It has occurred at least once to my knowledge that the vacuum signal was interrupted and the actuators slammed the doors open and closed, making a loud ‘rap’ noise, Occurring when the Fan, A/C was off.
-John

Hi, Open mind, thoughts wander to a random backfire through the Intake, or a thermally triggered event (like a Header “ping”) due to Thermal expansion, or a “pop”in the Exhaust due to an exhaust system crack up front, a leak, due to cool air being pulled in & colliding with superheated Exhaust gases?
-John