I need to tap your brains for ideas on what this whistling noise is. to give you an idea of what it sounds like, imagine a door not sealing very well when you're going down the highway only this noise rises and falls with rpm. A friend of mine said it sounded alot like alternator interference in a radio but my radio is off and still does it. It doesn't do it when the truck is cold only when the temp rises a little. Once its warmed up, I can be at a stop with the truck in neutral and slowly raise the rpm's and the whistling rises and falls in direct proportion.

I wondered if maybe it's the turbo but the noise seems to be more dependent on rpm than load. If I'm climbing a hill and accelerate, the noise doesn't really change as you feel the boost build.

Another bit of info: the whistling used to be more erratic until I changed the thermostat. Old one was stuck open so the truck never really warmed up. I also put a new exhaust manifold on at about the same time. I originally thought the whistle was coming from the grand canyon sized crack in the manifold but no such luck.

So I'm stumped and need some troubleshooting ideas. Oh, and the noise is very audible in the cab but not so much from outside with the hood open. Maybe a vacuum line inside the dash?

sorry for the long post.

 

Check your clamps on the hoses coming out of the turbo, also check and see if you have a break / crack in a hose.

 

Could it be the belt? Drip some water on it when the engine is running to moisten the belt and pulleys, see if it goes away. I had this happen on my Toyota car, the belt was getting old and glazed, and whistled like a drunk bum. Poured water on it and it quit, then of course dried up and did it again. Replacing the belt stopped it.
-P

 

You jogged my memory! The belt could be the problem.
I have friend with a GMC that makes noise caused by the belt, the shop can't figure out why but when it acts up a new belt corrects the problem, The pulleys are aligned up, bearings are good on idlers.
This truck was purchased new 2002 and they have never figured it out to this day,

 

Mine used to do that. fix with TSB http://dodgeram.info/tsb/1999/09-04-99.htm

 

that tsb sounds just like what I'm experiencing. I should have some time to try it later this afternoon. If that's not it I'll check the belt and the intercooler boots etc. as mentioned.

thanks for the help guys.

 

And the winner is.....gwatson!!! (and the crowd goes wild )

no more whistle with the heater hose clamped off, so I guess I'll get the replacement part. will be nice to drive the truck with one less irritant.

much appreciated!