Mine has also done this since I`ve owned it (with 17k miles) I`ve narrowed it down to either the A/C compressor kicking on for a split second at startup or it`s the ABS HCU (Hydraulic Control Unit) doing it`s test run. mine also only does it after sitting for awhile (days) and is also intermittent so it is very hard to figure it out! Like Joe says she hasn`t puked anything up yet, so I`m not worried.

 

I was going to say "I think it is the ABS system 'priming'" but "1 excursion camper" beat me to it! I noticed it is definitely from the drivers side one day when the key had been on for two seconds but the engine was off. Before I had heard it while the engine was cranking so it threw me off. It seems like the excursion has to sit for 24+ hours for the system pressure to bleed down enough to require a 'prime'.

 

Yes, ABS unit. It happens to me quite often as we do not drive it everyday. I will sometimes turn the key and wait a few seconds, then there it is (SNORT). Only after the truck sits a few days.

 

I'm another one with the noisy blend flap just after start.

 

Wow. I am not alone!

Based on the number of responses there seem to be a lot of us that have endured this behavior. I heard it for the first time this past week and immediately had nightmares of a failing cam or main bearing.

 

I heard it for the 1st time today on my X. I just cycled the key to start but didnt crank it up. Thats when I heard the sound. I definately came from the driver side near the front behind the driver side head lamp.

 

My daily driver is an Oldsmobile 88, 1995 vintage (80K). This thing does it as well, Friday when leaving work I just happened to place my foot on the brake pedal to slow for a speed bump in the parking lot and heard the noise and felt it through the pedal.