I was driving and heard a whining noise, when I increased or decreased rpms it quit. After I heard it the first time I kept trying to recreate and did but there was no rhyme or reason, different speeds and different rpms produced the sound and again when I increased or decreased rpm it went away. I have the Gotts mod and it did sound like air. Could it be because it is below zero and the super cold air caused the sound in some way? Truck seems to be running okay, all gauge readings are normal and it did not happen at first, truck was driven several miles before it occurred.
2005 F150 STX 4.6L Gotts EVO

 

check the foam around your airbox where the filter sits.

 

4.6s do not have the set up with foam like the 5.4 does.

 

It has the canister type filter but I will check around where it goes together and see if anything is coming lose. This cold snap brings out all the weak points in machinery, had to buy a new battery for my 8N.

 

My 2004 does the same thing. When it is below zero. I have determined it is the alternator. It is intermittent and the alternator works fine. I have not spent the money to replace the alternator, out of cheapness. Is your alternator the original?

 

Is the sounds like a whistle. Starts out gradually and disappears like with a gear shift. My 4.6 does it too, but only when it's super cold like below like 20 degrees

 

I assume the alternator is the original. And yes Bryan that is what it sounds like. Thanks for the input, sounds like it is a normal thing for the 4.6. My truck sits in the garage most of the time and I usually don't drive it in extreme cold temps so have never heard it before, have a '96 F250 that is the workhorse so that I don't put my F150 at risk, lol, I really like my truck.

 

Mine does it sometimes. Sounds like a baby turbo/super