Topic: Whats that noise on morning start-up?

[spider]

You know the one. A hollow air sound that continues for a number of seconds then abruptly stops. It just dawned on me what it is but I haven't verified it yet--perhaps tomorrow morning. Hint  (found in a current thread) D-oh

[Treeman]

Ummmm....... gas??

[MGar]

Fairly certain the noise is the ECM trying to raise the rev's with the TB closed to increase vacuum, combined with cold start procedures to get it and the cats up to operating temp.

[1LILNDN]

I had that but it turned out to be the Turbo Heat Shield would Vibrate until  it warmed up then stops. I watched it a couple times . It would Expand and tighten up.      was a real PITA

[Brad Kenny]

Have the same valve rattle noise at startup every morning that lasts for about 2 seconds on cold mornings. Personally, I go with very cold oil/engine reset for cold start. I have seen oil temps down to 6 degrees farenheit. It has never caused any problems. Just sounds horrible for a couple of seconds. I think we talked about this before here at KP Forum.

[DeepBlueGXP]

It's normal whether you're talking about what TreeMan said (stay away from deviled eggs and beer ) or your car.

It does a higher RPM warm up like MGar said and then settles down shortly after.

Normal!!!

[spider]

Definitely normal & we have all talked about it before, but what is it? I think its the vacuum pump omitted on the early '08 models that primes the brake booster. The electrical component mounted at the brake booster (attached to the one-way valve) probably tells it when to run/shut off. Guess its time to comb through the workshop manual.

[NormSky]

As McGar mentions, most GM cars have noisy IAC(ilde air control) on cold starts.

Pull the TB connect to and do a cold start to narrow it down if you think that is not it.

[spider]

The workshop manual ('07) says the auxiliary pump is only on the turbo models. Is that so? The NA cars do this noisy start also, correct?  The unit on the booster is a vacuum sensor. Using a stethoscope the vacuum motor was quiet except for one small burst as the sound disappeared. Don't know what to think now since the early '08 cars did not have the pump & were having hard pedal issues at start up I assumed this might be the mystery sound source.
 Not sure just how the idle air control would do it since the idle is still high as the sound abruptly stops. Cam phasing of some sort on cold start? 
   
 

[Imaj]

This happened to me too. It is an easy fix. When you get into your car after it has sat for awhile. (Your timeframe may very.) Turn the key to the on position. (Do not start the car!) leave it in that position for 15-20 secs. (It is your fuel pump.) Now start your car. You should not hear that awful rattle on startup.

[spider]

Different sound Imaj. Its like a loud exhale from the intake that abruptly stops with a chirp.

[Imaj]

Oh, I see. Sorry. Good luck sir.