About a month ago while changing oil and looking over everything I noticed my exhaust manifold was cracked. Thanks to @TFaoro who still had his stock manifold. I finally had time to get it installed yesterday. My manifold was cracked much farther than you could see on the truck. Here are a few pictures. 

Was it hissing or growling that you could hear?

A little hiss mostly towing when it would get hotter and open up. 

I need to check mine out,  I get a hissy also, but too lazy to look.

I'm curious to see the temp difference between the first 3 cylinders and the back 3 cylinders Monday when I get my Quadzilla hooked up. 

When I checked mine, 4-6 was about 50°F warmer and had (IIRC) 5-10 psi higher drive pressure at WOT than the front 1-3 cylinders.  This was with a fairly stock HX35 which has a twin scroll turbine housing.