Intake noise
 

I have a '96 F-150 300 I-6, it is making a load "whirring" sound at idle and is relative to throttle. It sounds like an amplified intake suction. Any suggestions or past similiar experiences?

Intake noise
 

You didn't mention any driveability problems such as rough idle,surging,etc.! Try removing the belt and re-start the engine.If that doesn't give you an answer,try pinching off a few of the AIR hoses one at a time to see if that makes a difference. Also,remove the intake hose from the throttle body to see if the noise gets louder or even quits. Let us know more as you go along.
Phillip

Intake noise
 

Sounds like you have a vacuum leak, check your vacuum hoses and/or try what phillip spoke about, by clamping on the hoses till you find the one causing the noise.

Dave

Intake noise
 

I recently had a similar problem. The sound was more of a whistling sound. I finally discovered the carbueretor nuts had loosened and thus the engine was sucking in air around the gasket and carb base. This seems to be a recurring problem. Make sure the carb mounting studs are tight in the intake manifold. Also, try thread-lock on the studs. If this is your problem you should notice an intermittent poor idle. Also, in my case the "whistling" was most pronouned at idle and changed pitch slightly when accelerated. Hope this might help.
Mark
pracklam@usa.net

Intake noise
 

Check out the post on ventura effect tubes. I wonder if yours have been removed? Did you buy the truck used? I have a 96 4.9 also. I am not sure what these things even look like or where they are located. One guy thinks on the 4.9 that they are part of the air box. Is your intake all stock and complete? There function is to quite the intake noise buy restricting the air flow. When I get a chance, I will check mine out.
Chris

Intake noise