1999 K2500 454 4WD Suburban Air Injection Noise On Start Up

[Ricetuner]

Two weeks ago I noticed a pronounced whine (similar to an a/c compressor clutch failure or belt squeal) coming from the motor on hot starts. This noise is only present for 30 seconds to 2-3 minutes and only occurs on hot restarts, apparently when the air pump is "on".

Upon further inspection, I determined that the noise was coming from the air injection "air valve" which splits the air pump outlet hose to the two hoses going to the exhaust check valves. The "air valve", GM P/N 12550930 has what appears to be a diaphragm on it, for what I do not know. I am not a GM tech but this looked pretty simple and I assumed the valve was failing (I sound like one of my customers). I installed a new valve and low and behold the noise was still there. In fact, the noise may be a bit subtle sometimes and more pronounced at other times.

I purchased this vehicle 4 months ago with 57,500 on it. Single owner, immaculate, stock. It now has 61,000 miles on it. When I purchased it I went completely thru it. I had GM perform a complete 60K with all fluids (transfer case, diffs, coolant, brake, etc.), filters, pcv, cap/rotor, plugs, and performed a VCM software update. In addition, I had a Magnaflo muffler installed and rear air suspension (I pull a toy hauler to the desert), Runs great, tows great. Has not been back to the dealer since I bought it 3,500 miles ago (until today). No MIL lighting, nothing, just the noise.

I took it into GM today and the word I'm getting it that this is normal for this vehicle and nothing is wrong, it's normal noise when the air pump is running, come pick up your vehicle. In fact, they told me that they had done exactly the same thing I did (replace the air valve) when these started showing up with the noise. I find this hard to believe or my air pump has been non-functional for four months.

I have driven this vehicle exclusively for four months, have good ears, have 30 years experience in the automotive industry and know that this noise has not been present prior to two weeks ago. Oh yes, no sign of heat (failed check valve(s)) in the air valve to exhaust check valves hoses.

Looking for some feedback here, hoping someone has some input.

Thanks!