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Pun totally intended here, stay cool man. You asked for help diagnosing this sound and this is what help looks like. Lots of experience is chiming in on this one.
 
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Sounds like that are hard to diagnose in person, even harder online. You may have to take it in if you still can’t identify it. 🤷‍♂️
 

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You mean the vents from where the AC air comes out?
Yes. Try using button #4 to cycle through the four different blend door positions and see if you can replicate the sound.
 

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Discussion Starter · #26 · (Edited)
Yes. Try using button #4 to cycle through the four different blend door positions and see if you can replicate the sound.
What is weird about this sound is that it starts at the same time the needles of the dash move. Why do you think this sound is caused by a stuck blend door?
 

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Hi everybody. I am looking for your knowledge and help. My Infiniti Q50 Red Sport that has 5,000 miles makes this single loud weird thump noise when starting the car cold first thing in the morning after the car has been parked for several hours, it never happens at other times. The sound appears at second 7. Is this normal?.

This is the video

I actually have the same exact sound happening in my RS, in the same exact spot and under the same conditions you mentioned, and I’m at 68k miles. I never thought to look into it as it doesn’t effect anything I’m aware of. I’m bringing my car in for a scheduled service soon and I’ll mention it. I always figured it was part of the AC, as it sounds like something opening. Maybe something is catching?
 

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Discussion Starter · #28 ·
I actually have the same exact sound happening in my RS, in the same exact spot and under the same conditions you mentioned, and I’m at 68k miles. I never thought to look into it as it doesn’t effect anything I’m aware of. I’m bringing my car in for a scheduled service soon and I’ll mention it. I always figured it was part of the AC, as it sounds like something opening. Maybe something is catching?
You have the same exact sound?. Can you upload a video?
 

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You have the same exact sound?. Can you upload a video?
I’ll upload a video tomorrow, as it only happens from cold start and I’ll be out and about tonight. It might do it when I get off of work (as I work graveyard), but I usually only get that sound when it’s been sitting for a long while, roughly 12 hours or so, give or take. I hear mine from the left side, almost center dash.
 

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You have the same exact sound?. Can you upload a video?
Also, my girl says she actually feels the thump under her feet on the passenger side floor, but I’m doubting that’s where it’s at. I truly believe it has something to do with AC. I’ll upload a vid soon and keep you posted about what I find out, as I want to know now.
 

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What is weird about this sound is that it starts at the same time the needles of the dash move. Why do you think this sound is caused by a stuck blend door?
I'm just spit-balling here. If you don't know what it is, start eliminating what it isn't.

I don't suppose you've had the car scanned for DTCs? If there are any current DTCs, it would help to know what they are.
 

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Discussion Starter · #32 ·
I'm just spit-balling here. If you don't know what it is, start eliminating what it isn't.

I don't suppose you've had the car scanned for DTCs? If there are any current DTCs, it would help to know what they are.
They scanned it in the dealer and there are no codes stored. Do you recommend telling the dealer to change the blend door actuator?
 

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2018 Q50 Red Sport 400 AWD
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How about leaving the car at the dealer, let a tech cold start it, and see what they think it is?
 
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How about leaving the car at the dealer, let a tech cold start it, and see what they think it is?
Great minds... (from the same discussion in our sister forum):

Water Rectangle Font Circle Electronic device
 
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Discussion Starter · #36 ·
Going down a different rabbit hole...

To me, it sounds like a blend door is stuck, so the sound is the actuator trying to move the blend door into position, and can't.

Try the A/C in different modes and see if the sounds repeats to confirm.
I tried moving the AC in different modes and the sound does not occur. If you notice in the video the noise occurs at the same time that the dash light lowers. Is it normal that the dash light lowers like in my video at second 7 after starting the car?
 

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Discussion Starter · #37 ·
I tried moving the AC in different modes and the sound does not occur. If you notice in the video the noise occurs at the same time that the dash light lowers. Is it normal that the dash light lowers like in my video at second 7 after starting the car?
 
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