I had the strangest noise today at start up on our new 06' with 2000 miles on it. I fired it up and I hear this sound like a pop off valve going off with a shewwwish sound. It was like pulling the lever on a water heater, a kind of a pop then shuwwwishhhh. My wife was just walking around the passenger side by the front right tire and said it emitted a water like vapor cloud from inside the wheelwell and fogged the driveway with water droplets by the tire.
I looked in side but its dark now so I'll half to take a closer look tomorrow.
I'm thinking AC condensation valve ????
Anybody got any ideas ??

 

Ineresting I just heard a simmilar sound today...I will be following this thread.

 

I always park the truck with the noise pointed down. Coincedentally, this helps drain the AC. Might be why I haven't heard this sound.

 

Did you have the A/C on? If you did I bet it was the High Side Pressure relief valve on the back of the compressor. My truck has spiked the high side pressure when you first crank it up but it kicks off the compressor perty quick until I get rolling. Here is how to check. Look at the back of the compressor. If you see a yellow oily film around the relief valve that is what happened. The high side pressure spiked, the high pressure switch did not turn the compressor off, and the relief valve opened up spraying oily refrigerent all over the place. I have been working with Beemo on my A/C issue on the 03 a/c thread in the No engine or drivetrain forum. Maybe you can post a question to him so he can give you an answer if this is what happened.

 

Rite on Spooler, This sounds like what it is. And yes the AC was left on, and started with it still on. I'll be checking under the hood looking for what you said.
Thanks for your time to post a reply.
Joe