Strange Noise

Tiny
ENVOY04
  • MEMBER
  • GMC ENVOY
I own a 2004 GMC Envoy SLT, 54,000+ miles, 6 cyl.
(bought it new)
For the past several weeks whenever I start it, in the morning or after work ( I assume it must be completely cooled down to happen as it doesn't happen any other time) I hear a noise that sounds like a hydraulic lift that lasts about 15-20 sec. I asked the service department clerk when I took it in for it's 54,000 mi service, and was told it was the "moisture compensator" due to the hot weather we've had here in Virginia. This is the 4th summer I have gone thru with it and this is the first time I have heard this noise. There has been no diminishing in performance, and no lights on the dash.
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Saturday, August 18th, 2007 AT 5:44 PM

3 Replies

Tiny
CLY
  • MEMBER
Sounds like maybe the secondary air pump. The pump is mountd to the frame rail under the truck just below the drivers seat. You could start it up and place your hand on the pump and see if the noise is coming from it. I have seen several times where these pumps get water in them. The hoses that go to it have retainers that you can push in with your fingers to remove them and see if any water runs out. Another thing to check would be the level-ride compressor. It could have a rock up there by it rattling around or a bent shield or something. It is located on the passanger side frame rail towards the rear of the vehicle.

Hope this helps.

Cly
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Sunday, August 19th, 2007 AT 5:56 AM
Tiny
ENVOY04
  • MEMBER
Thanks Cly, But if it is water in the secondary air pump, why then does it only happen after the vehicle has sat for several hours and not under normal "stop and shop" use? And how can an air pump sound like a hydraulic lift?
By the by has anyone else heard of or know about a "moisture compensator"?
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Sunday, August 19th, 2007 AT 10:11 AM
Tiny
CLY
  • MEMBER
I have never heard of a moisture compensator. I was tring to think of things that run during cold start. The secondary air injection pump runs its test on start-up when engine temps are below a certain temp. If the engine is above the temp required then the test does not run.

Cly
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Sunday, August 19th, 2007 AT 8:32 PM

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