NEED HELP! Hissing from intake!

[PresidentV8Fan]

Ok, not my car first of all (240 owner though )Buddy at work has a 2003 Nissan Altima bone stock. Said on Saturday his car started making an odd hissing sound. After talking to him for a while about it, it only happens when the throttle is pressed 50% or more...sound of the hissing increases with throttle pressure.Aksed if I wanted to take it for a spin real quick, see if i could identify it. Took it around and IMMEDIATLY was stunned at how loud it was. Full throttle sounds like some just shot a tire...Sounds like 50 PSI leaking from a tire, its that loud..It is a hissing sound, not a sucking sound, it does happen at 50% throttle and does increase with throttle and RPM.Power seems to cut out a LITTLE towards the top of the RPM band but if you were just driving it, I dont think youd notice it all that much. I was looking for something like that so...Anyway, it does this even in neutral and from the sound seems to be coming from the air intake box, but since hes drive by wire I cant tell by myself, on my break I think I'll mess with it a little more, but does anyone have any suggestions on what it could be?Cracked piping? Cracked intake manifold? Hole in a vacuum line? (though that doesnt make that much sense for that much noise)

[08altima35]

if it's loud enough and it's making the sound while revving in neutral, you should be able to easily locate the leak. also, i doubt it's coming from the stock airbox, but don't rule out anything until you find where exactly it's coming from.

[PresidentV8Fan]

OK, took a closer look at break, had someone else rev while my head was in the engine bay...I was mistaken, it is not coming from the intake side at all it seems. The hissing is coming from the either the headers/downpipe or the head...maybe.Since the car still has the heat shield on its quite hard to tell, and once I found out it was basically a massive exhaust leak (you can definatly smell it too) I decided not to mess with it to much as its not my car and turned it off.

Has anyone heard of this before though? What should happen first...take off the heat shield and turn it back on? Or possibly do some type of foaming through the car (I forgot the actual term, and I know its not healthy for the car persay...but I can garuntee that white smoke would come from the hole, lol)Ideas?