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Join Date: May 2013
Location: Picton, Ontario
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Help me diagnose noise behind dash

I've had a rattling noise coming from behind the dash in my '88 3.2 for some time now, and it's getting worse so about time I looked at fixing. I've included a video to demonstrate the noise - here's the rundown...

Car does not need to be running or moving
Noise starts as soon as key gets to 'ignition 2' position
Seems to be coming from directly behind HVAC control panel
Pushing on panel will slightly alleviate the intensity
When driving, cornering has an affect on intensity as well - sound lessens under hard cornering
I've removed the ashtray - no change

https://www.youtube.com/watch?v=SXbyMJlQQmE

Does anyone know if there's a small fan/blower behind the panel that runs all the time that could be giving me trouble? Again, car does not need to be running, and noise happens with all HVAC controls off. Just looking for insight before I start tearing things apart.

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Old 09-21-2014, 07:47 AM
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Hi - your video is setup as private.
Yes, there is a fresh air blower in the area.
Open the trunk lid and listen for it behind the black hardboard under the windshield. See if you can hear it there as well.
I forget what switch turns it off :-)
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Last edited by steely; 09-21-2014 at 08:09 AM..
Old 09-21-2014, 08:06 AM
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Do you have auto heat? There is a sensor under the ashtray, behind the center console that has a little fan associated with it. On my '87 the fan turns on at position 2 and you can definitely hear it.
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Old 09-21-2014, 08:53 AM
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Time to open the frunk and start the listening diagnosis. At the very least you should take the carpet out, and then the cardboard at the back. A flash light and some feeling around in there should located that noise pretty quickly. I'm guessing Fresh Air blower...
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Old 09-21-2014, 09:27 AM
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I bet it is the temperature sensor
Old 09-21-2014, 09:35 AM
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Quote:
Originally Posted by steely View Post
Hi - your video is setup as private.
Thanks for the replies, everyone! The noob has fixed the link :roll eyes:

I'm pretty sure it's not the fresh air blower, because that's what's activated by the top, right hand lever, correct? I have ensured that nothing is turned on, and I can clearly hear when I turn on that blower.

I do have auto heat, so if there's a fan attached to that, I'm betting that's it - my brother had this problem in an early 90's BMW as well. Do you know if you can access that sensor from the frunk?

Cheers!
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Old 09-21-2014, 11:54 AM
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Sorry, took a football / tv break. Yes, the fresh air blower is activated. I am not sure that the sensor would be causing the noise unless it was rattling around. You might be able to access it from under the dash if not the little vent plug itself behind the steering wheel just to the left of the heater controls on the dash. I am attaching a very nice figure from Ian McArthur from some time ago.
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Old 09-21-2014, 02:20 PM
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Great pictorial of the HVAC system Dan, thanks for sharing/posting it.
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Old 09-21-2014, 02:45 PM
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Quote:
Originally Posted by blotto649 View Post
I do have auto heat, so if there's a fan attached to that, I'm betting that's it - my brother had this problem in an early 90's BMW as well. Do you know if you can access that sensor from the frunk?
Cheers!
The sensor is not in the frunk. It's in the cabin under the dashboard. The easiest way to find it is to follow the black tube that runs from the round vent to the right of the steering wheel and to the left of the HVAC controls. The tube attaches to the back of this round vent and runs down to the sensor.
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Old 09-21-2014, 03:02 PM
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For pictures, check out this thread.
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Old 09-21-2014, 03:05 PM
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I listened to the video - that is odd. I can't tell what type of head unit / radio that was - does it have a cassette tape player in it? It sounded like a capstan going bad.
I can't tell if it was related to the air blower or not either, like a leave trapped in the fan. Hopefully someone else can listen.

As mentioned before, see if you can hear it in the frunk too.
Perhaps try removing one of the instruments (clock maybe) to see if that gives you a clearer path to the noise - check first on how to do this - sorry I can't recommend the exact method.
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Old 09-21-2014, 03:24 PM
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Seconded on the Autoheat sensor. Sounds exactly like mine used to. It's held in place behind the ashtray with two tiny Phillips screws. You don't have to unscrew it to disconnect the plastic block of a wiring harness that powers it. Try pulling the electrical connection and see if that solves the mystery.
Old 09-21-2014, 05:27 PM
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I just watched your video. Sounds exactly like my car. That's got to be the auto heat sensor, the little fan associated with it.
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Old 09-21-2014, 05:48 PM
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Hey, my car have the same noise. Have you diagnosed the problem yet? Subscribed!
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Old 10-04-2014, 01:48 PM
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Sorry for the bump; I thought this was the correct diagnosis, I had the same sound. I pulled the small fan mounted to the rear of the ashtray which was full of 30 years of crud (see picture). The noise is still there, it seams to get higher in frequency as the revs increase... any thoughts?


Last edited by Alister_AU; 05-14-2017 at 11:28 PM.. Reason: Mistaken diagnosis
Old 05-13-2017, 07:28 PM
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