So, I've been noticing that while driving I'm hearing a whistle sound that appears to come directly from the throttle/intake area of the engine no mater what speed I'm going or what rpms the engine is running. It only is heard when the accelerator is pressed about 20-25% down. Give it a little more gas or back off and it goes away but bring it back to that 20-25% range and it continues.

I have checked all of my acc, power steering, water pump, and alternator bearings and they are all fine. I also took a look at all of the vacuum lines and replaced a few weathered ones but it hasn't gone away. The intake manifold gasket was replaced when the HG's were done a few weeks ago.

I have been trying to figure this one out for a few months now and have had no success. It is difficult to pinpoint where it is exactly coming from as i have not been able to make it whistle when the truck is in park and revving the engine.
Does anybody have any ideas?

 

PCV lines from both valve covers. One on throttle body side goes to TB rather than intake manifold.

 

Both PCV lines are new

 

When I pulled mine out the throttle body inlet for the hose was full of gunk. There is also an oil separator on the passenger side, which may be blocked.

 

I can't imagine they would be clogged with gunk when the entire top end was rebuilt less than 500 miles ago, but I can check them out.

 

Something might have fallen in somewhere while the top end was being rebuilt, and it could have very easily found its way their and clogged it up. I dont know about everybody else's experience with engines, but I have a really hard time keeping anything from getting into the engine while taking it all apart. Every time I have had an engine halfway apart it has gotten a little something in it.

 

since you had an overhaul so recent sounds like something got left loose or was not tightened properly and came loose or a bad gasket/ improperly installed one

i had a vacume leak and it was the line comng out of the drivers side ov the plenum towards the back that goes to the fp regulator

 

It made the noise ever since I got the truck. Even before the rebuild

 

Is there a horn on the front of the airbox? If missing it whistles.

 

Yes, there is a horn on the intake of the airbox