At times when I start my truck there is a hiss or a whistle like sound at idle. The engine makes too much noise when i open the hood so I can't find the location of the noise. Inside the cab it is very obvious.
When I start to throttle up the noise goes away and the normal whine/whistle of the turbo kicks in.
Any ideas?

 

wat year is ur truck? do u have the high idle mod? cos the louder noise could be from ur high idle mod. after the mod kicks in, to disengage it, jus tap on the brake, and the rpm goes back to normal.

tat must be loud if its obvious in ur cab. i'm jus saying it could be the high idle mod. it could be something else. if u dont mind me asking, kind sir, where is ur general location?

 

my truck is a 2003. The sound is present when warn too. No high idle mode when problem shows up.

 

Doubt its anything with high idle, need to check all 4 of your intercooler boots and your up pipes

I just had to replace my up pipes on my truck kind of sucks doing it, mine had a crack right in it do you have a boost gauge?

 

How new are you to this truck? If it's new to you, no sweat. It's the turbo! Do you have the cat removed? Louder whistle yet, esp at idle! Nice isn't it? 2003's had a louder (more pronounced) than later models.