Diagnose This Noise Please

[Focker]

Hi all...

I just bought a 1988 GMC Sierra SLE (5.7L TBI V8) and I have a question for you gurus.

 

When I turn the key (but don't start it) I hear a noise coming from the passenger dash/kick panel area that sounds like a power antenna motor. The thing is it doesn't have a power antenna. The Chilton manual that I have doesn't say anything about power antennas anywhere.

 

Oh...It makes the same noise after shutting off the truck.

 

Thoughts?

 

Thanx!

[cerbomark]

try moving the vent direction selector and see if it changes anything.

[trucc_boi]

we had one at work that had a/c blower motor or something that would sit there and tick (very loudly) whether the a/c was on or not.. maybe it is a similar problem in the a/c system..

 

are you sure it's not a fuel pump or something coming on?

[gvbhunt]

I vote blower motor. I bet it is made to run whether or not the Heat/AC are turned on or not. For circulation reasons. That fan is down by the passengers feet if I remember right. Now why you would hear anything there when you turn the key OFF, that part confuses me. Truck built in 1988 does not have RAP I do not believe. How long do you hear it after you turn the key off?

[dlewis1111]

Hi all...

I just bought a 1988 GMC Sierra SLE (5.7L TBI V8) and I have a question for you gurus.

 

When I turn the key (but don't start it) I hear a noise coming from the passenger dash/kick panel area that sounds like a power antenna motor. The thing is it doesn't have a power antenna. The Chilton manual that I have doesn't say anything about power antennas anywhere.

 

Oh...It makes the same noise after shutting off the truck.

 

Thoughts?

 

Thanx!

 

Blower motor that runs when the key is on. Designed that way for positive ventilation all the time.

[Focker]

Excellent feedback with the fast replies guys...I forgot to select instant notification so I missed these.

 

Here is some more info:

When I turn the key to the on position it runs like a power antenna motor or fuel pump for about 4 seconds...You never hear that sound again until you shut off the truck and again it runs for approx 4 seconds whether the heater/AC power is on or not. I think it's heater/AC related because it sounds like it's coming from the area in the pic below.

 

I'm not worried about it..I was just curious as to why...I've had an 89 Blazer and a 98 Chevy extended cab and neither one did it.

 

 

[gvbhunt]

You are looking at the back of the blower motor there. Maybe the bearings are getting loud or the brushes are noisy when the motor is spinning up or down? I had a 1980 Grand Prix that the blower motor "ticked" when it was on low speed (which is also the speed when the AC/Heat was off). You would hear it tick loud until it got up to speed and hear it tick until it stopped spinning when you turned the key off.

[trucc_boi]

ours would sit there and tick for about 30 seconds to a minute after the keys were out of the ignition as well..

 

i think we just unplugged it/pulled the fuse and rolled down the windows (basically i wouldn't know what a good fix would be.. in texas most people pretty much need a/c but it was just a work truck and we toughed it out.. truck had power windows)

 

i do remember kicking the shit out of it one time and it stopped, but i think that was a coincidence because it came right back on next time we started the truck.

[Focker]

i do remember kicking the shit out of it one time and it stopped, but i think that was a coincidence because it came right back on next time we started the truck.

 

I'm going to shoot a quick vid with audio...Yes I'm that bored.

[Focker]

Here's a poor quality video where you can hear what I'm talking about. At first it's hard to hear over the chime signal but when I turn the key off you can defenitly hear it.

 

Thanks for all your help.

 

Clicky - Diagnose This Noise

[Focker]

I found the culprit. I unplugged this box and BINGO it stopped...But I don't know what it is?

 

I removed the blower motor for cleaning and tested for the noise again and it's coming from this thing behind the blower motor housing...In fact it seems attached. I looked through the Chilton for a description and it Chilton sux.

 

[Focker]

*** UPDATE ***

 

It's a little motor that opens (or closes) a vent once you turn the key on. Obviously when you turn the key off it closes (or opens). I got under the dash again and had a helper turn the key and I could see a white flap open and close. My Dad thought earler today (Before my joining of this forum) that it was type of heater vent. I guess my Pop is smarter than I remember...I always new he could beat up your Dad!

 

Now to figure out why (Just for the heck of it...I like to learn things like this).