[Richo]

Just today when I turned my 2013 Impala off, a knocking noise was coming from the dash and continued for 1-2 minutes after the car was off.

I started the car and it started back up but at a faster pace, but stops momentarily every time I adjust the vent. The speed of the fan seems to have no effect on it.

Does anyone know what the cause of this is? Here is a video of it:

 

[dj3]

Just from the video, I suspect the A/C blower.
Take the car to a knowledgeable mechanic or A/C shop.

 

[raylo32]

Man, having the noise with the engine off is weird. It could possibly be an issue with one of the HVAC dampers that are vacuum operated... hanging up and oscillating or something... that finally becomes quiet after the vacuum system leaks off? Just a wild guess. With the engine running operate the system in all its different modes and airflow directions and see if all the vents are functional and working in accordance with the switch positions.

 

[ukrkoz]

I'm with Raylo. Something is flapping.

 

[Brainbucket]

That is a mode door electric actuator. The reason I know that is you move the mode setting and it quit. The gear is stripped. Replace the actuator and your good.:vs_cool:

 

[Richo]

It definitely is related to the AC. It hasn't done it since the day I posted this, but I have not run the AC. Today I accidentally bumped the AC button when adjusting the fan and it started up as soon as I turned the AC off. As long as the AC runs it does not do it, but after turning off the AC it does it for a minute or two before stopping.

 

[raylo32]

It's trying to shift a door position when you turn off the A/C and seems to be grinding its gears. Since it happens with turning A/C off it might be a door on the evaporator box.

Interesting, the last ones of these I worked on were vacuum operated, but Brain said this one is electric. Makes sense they could create electric servo motors for this purpose. Should be an easy repair IF you can get to it without major disassembly.

It definitely is related to the AC. It hasn't done it since the day I posted this, but I have not run the AC. Today I accidentally bumped the AC button when adjusting the fan and it started up as soon as I turned the AC off. As long as the AC runs it does not do it, but after turning off the AC it does it for a minute or two before stopping.

 

[Richo]

Yeah, that's a big IF :vs_laugh::vs_laugh::vs_laugh:

It would appear to involve disassembling the dashboard. Sounds like it's above the glove box. Air bags in there too though, so not so sure I would want to start digging. :surprise:

 

[raylo32]

Whatever you do, before digging around in there disconnect the battery!

Yeah, that's a big IF :vs_laugh::vs_laugh::vs_laugh:

It would appear to involve disassembling the dashboard. Sounds like it's above the glove box. Air bags in there too though, so not so sure I would want to start digging. :surprise: