question on a powerstroke

Ok I have a 2000 F250 with the powerstroke in it. Right now about 100K on the odo. and just needing some info. In the morning when its cold and I start the thing up and leave it running for a few minutes to warm up. If you go to the exhaust it sounds like a big air pump is letting off pressure. If you touch the gas and rev the engine and let it return to idle it stops. It only does it in the morning when the engine is cold and stops after it warms up. The truck runs fine, starts fine and everything works fine. Just wondering if maybe it could be something getting ready to go bad. Oh yea it also has an aftermarket exhaust on it if that might have anything to do with it. Any help or thoughts would be app.

Nope, that NORMAL.

Waht you are hearing is the Exhaust Back Pressure (EBP) system working just as it should. It is installed to aid in quicker warm-up by placind a "load" on the engine using exhaust back pressure for the engine to work against.

The EBP should be off with coolant temps over 120*F (or so), throttle above ~25%, when the ambient air is over about 40*F.

Yup, all systems are a GO!!!

I've got straight dual pipes and my truck does the same thing on start up when it's cold.

Thanks guys I was kinda worried when I first heard it and just wanted to ask. Never heard it before, but then again I've never owned a powerstoke before this one. Kinda cool system huh? Thanks again.