hmm, this sounds really familiar... I know exactly what it is... issed:

Its the cylinder pressures bleeding back into the degas bottle and whistling through the cap. aka... puking

but... its all fixed now. Headstuds, new gaskets, egr cooler, and I blocked my up-pipe going to the EGR cooler. problem solved!

I have run my truck harder then ever and it is running flawlessly!

 

Its actually boost pressure escaping and hissing.

 

Cool info there Great Green One !

Got anything on the Excursion driver side wind noise....

ONLY compaint about the 3 Ex's I've had...
can hear wind and road noise near my left ear....