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
 
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no load on the engine. i am going to drive it a little more to see when it actually happens. It does seem to happen every time I leave my driveway. I drive real slow to the end of my driveway, 1000', then accelerate until I hit third gear. I let off and it will usually occur shortly after that. seems to happen after i start to coast but I will pay more attention to this.
 
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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
 
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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

wouldn't that cause other issues