1999 Chevy 6.0L Vortec whistling problem

[Kobies Kool 40]

My Dad and I are trying to troubleshoot this whistling sound in the cab.  It changes pitch with the rpm's and you don't really notice it until about 2000 rpm.  It kind of sounds like it's right underneath the dash.  We have ruled out heating, cooling, exhaust, radio and am running out of ideas.  It's weird, when you sit on the passenger side it almost sounds like it's behind you.  The sound stays the same if you're on the road or sitting in the garage.  Dad thinks it has to be something vacuum?  There have been no modifications to this truck.  Any ideas?

Thanks,

Shawn

[model a vette]

I sometimes get a whine like that thru the speakers. I think it is an electrical noise problem with the alternator. I plan on hanging a large capacitor on the alternator output to see if that cancels the noise. You might try one of the large auto stereo shops for a capacitor.

[Crosley.In.AZ]

there was a service bulletin on noises caused by the water rushing through the heater core.

Seems like a restrictor plug was placed in the heater hose

[Kobies Kool 40]

Thanks for the ideas, we have not narrowed it down to any one specific thing yet.  Has anyone heard about the throttle body whistling, Dad was listening through the pipe and moving around while I held the rpms steady at 2000 and he said that when he got close to the throttle body was when he heard the closest thing to what we are hearing in the cab.  What could go bad in the thottle body that would starting whistling?  Thanks again for the feedback, much appreciated.

Shawn

[enjenjo]

Base gasket can blow out.

[Crosley.In.AZ]

Base gasket can blow out.

Are you thinking the old TBI stuff?

This truck should be a LS1 motor with a dry intake, fuel  injectors at the heads.

Check the inside of the throttle valve blade area.  A good cleaning with carb spray is needed every 30k miles or so.

[Kobies Kool 40]

there was a service bulletin on noises caused by the water rushing through the heater core.

Seems like a restrictor plug was placed in the heater hose

Crosley, my Dad finally got this fixed and this was the problem.  Thanks for the info