What is this sound from the dash?

[George7941]

I get this sound from behind the instrument cluster of my Sierra every time I turn the ignition on or off. On turn-on it last for about three seconds (about half a second longer than the fuel pump, and, no, the sound is not from the fuel pump; sound is there even if if I pull out the pump relay) and on turn-off, it lasts for under a second.

The sound is like that of a small motor whirring away, somewhat like the sound of electrically-actuated climate control doors. My climate control is all cable-operated, with no motors.

The truck is the one in my signature. I cannot figure out where this sound is coming from. The sound might even be from a vacuum operated device.

 

[JTK]

George, that's just the motorized tachs GM's has been using since ~2002 or so. You get kind of a *hiss-click* on shut down. Perfectly normal.

Joel

 

[outshined]

It could be the ABS running its "self check". If that makes sense.

I have an 03 Silverado and IIRC the sound or "purr" is mentioned in the owners manual.

Take it for what it's worth. I'm sure others will jump in.

 

[George7941]

Just went out to my truck and checked again. On turn-on, the 'motor' sound slows down after a second and a half, as if positioning something into place and doing the final fine adjustment.

It sounds like the tach, as Joel mentioned. But there is definitely no click on turn-off and the sound is somewhat of a hiss, the way it rises and falls on ignition turn-off.

Outshined, I checked my Owners' Manual and it mentions, under the ABS section, that the ABS system conducts a check and the driver might hear the ABS motor or relay. But this is only once you drive off, not from just turning the ignition on.

Joel, just curious. Neither of your present cars are GM, and I remember your previous 'babe-magnet' Windstar. How come you know so much about GM tachs?

 

[JTK]

Originally Posted By: George7941
How come you know so much about GM tachs?


I had a 2005 Trailblazer with the exact same 'feature'.

Joel

 

[RoGuE]

Yeah, I hear this in our 2002 Suburban. When you shut the engine off you hear a very faint noise like a small fan. It keeps going until you open the door though.

 

[George7941]

Your noise must have a different origin because my tach noise has nothing whatsoever to do with the door.

 

[bigmike]

I have a noise like you describe when turning the ignition on - I've assumed this was the fuel pump but maybe I'm wrong and it's something else. Done it since new.

I don't notice anything at shutdown other than it sounds like an air brake let off but much quieter than that. Just a whooshing noise, I guess.

Now if someone would tell me why my truck sounds like birds chirping when going over uneven pavement, that would be much appreciated. I'm pretty certain it's shock bushings or something suspension related. Spent hours under the truck and can't seem to find anything though.

 

[George7941]

When you are inside the truck, with the windows closed and your seat belt on so that the chimes dont come on and drown out other sounds, you will hear the tach well and the fuel pump faintly. You can hear the fuel pump shut off about half a second before the tach shuts off. The tach noise, on shut off, sounds a bit like air brakes because it rises and falls.

If you really want to hear the fuel pump, park next to a wall and keep your driver side window down. Then you can judge whether the pump sounds normal or whether it is unusually loud, which is a sign of impending failure.

I don't have any unusual sounds from my suspension, so I dont know where your chirping sound is coming from. You can try spraying all the bushings with silicone lube and see if it makes a difference. You could try disconnecting the shocks. If nothing works, you could always buy a set of Chassis Ears and track down the noise.