Alright 2004 F150 4.6 75,000 miles. It has been cold here in PA for the last couple weeks. Last wednesday i put a throttle body spacer on (i know they are a waste but i put one on anyway) And that night the wife and I went for a drive and she asked what the high pitched whistle was that came with throttle and went away when i let off the throttle. I couldnt hear it but i told her that i put a throttle body spacer on (she didnt know what i was talking about) and that some of them whistle and almost sound like a turbo on a deisel. So i continued to drive it a couple days and then we went somewhere again and right after i started the truck backed out the driveway and went up the road I finally heard it, real high pitched whistle that showed up at the high RPMs of first or second (cant remember which and went away with the shift and drop of RPMs) gear while first accelerating. After that initial cold start high pitched whistle at the first high RPMs while accelerating it is gone and disappeared. Now since that first time i heard it, i removed the throttle body spacer thinking it was the cause of the whistle. But the last two mornings after i removed the TB spacer i get the loud whistle on the first high RPMs during acceleration and then gone. Now this only started after i put the throttle body spacer on and after. I read a few posts about it, maybe i need to check some of the connections on the air filter box and tubing going to the TB. That is the only thing that i touched last wednesday when puting the TB spacer on. Anyone have any other thoughts?

 

I don't know if this is the same thing but I had a whistle at certian speeds when it was really cold out. It was the alternator. I had it replaced under warranty.

I know some others had the alternater whistle too but not sure if it's the same as the problem your truck has.

 

After i read alot about the alternator whistling i think that might be it, in any case, im going to take it in cause wether its my alternator or PS pump its all covered under my extended warranty. But any advise or knowledge is greatly appreciated.

 

Well i take it in on Monday and they are going to replace the alternator (if that is what it is) and fix a rear axle seal out by the wheel. All covered under my extended warranty, so hopefully the whistle is the alternator liek everyone says. Any more input?

 

My 04 has the whistle too. It's the alternator I would bet.

 

Another cold start last night and the whistle, and another cold start this morning, it would be very audible when the RPMs hit a peak right before a shift, and then when i was cruising at 45 it did it constant for a couple seconds and then disappeared and then the truck was warmed up and didnt do it again.