Damn Cold Start Noise?

[5.0 Mountaineer]

Whenever the weather is around or below freezing my truck makes a loud ssssshhhhhh noise. Then after about 10 to 15 seconds it makes a noise where it sounds like something engaged and the noise stops. I've read all the posts about the timing chains in the SOHC motors but I have a 5.0. Its hard to tell what it is because it happens in such a short period of time. I haven't gotten around to taking of the serpentine belt yet. I was wondering if you guys had any suggestions on things to check. The truck has 73,000 miles and I changed the oil about a 1,000 miles ago. Thanks, Steve

 

[Nate1]

Vacuum leak? Are you sure everything (all tubing) is seated well, and all bolts are tightened to spec? I'm not sure, sounds weird.

 

[5.0 Mountaineer]

Everything looks ok there is no hissing after the first couple of minutes. So I doubt its a vacuum leak and it idles almost perfectly at around 700 rpms.