Hey guys, I know there is a bunch of threads covering the various whistles and whines from this engine. However, after following the advice and some maintenance, the whistle keeps coming back. My truck has the 5.4l motor at about 235XXX Miles. The whistle/whine starts when the motor is idling at 500-600 rpm when in drive gears. Even in reverse, drive, and low gears. But when I accelerate or traveling at a constant speed, there is no whistle. The only time the whistle starts when the truck is moving is when I push the brakes and the RPMs drop to the 500-600 rpm range. The whistle seems to be coming from the front of the motor/ belt and pulley area. I've already replaced my PCV valve, I've replaced my belt tensioner, and my air intake system seems to be pretty good shape. I'm at a complete loss of what it is and when I take it into the shop, the whistle never starts for him. The noise is not affected by temperature or weather. I live in Arizona and it has happened in winter and summer. Any advice would be great! I also have a short video of the issue but I can't attach it.

 

I had a similar whine on my 70 Mustang 302 V8 way back when and it was the alternator. It was diagnosed by a really smart old mechanic who put a very long screwdriver on different parts under the hood and the other end to his ear.

 

Yeah I got a mechanics stethoscope which is a civilized version of the old screwdriver trick. Just checked my alternator and it isn't making the noise, neither is the throttle body. I'm baffled at this noise.

 

Interesting, I was gonna say alternator too. When I put my new alternator in it gives a whistle similar to what you describe.

 

A whistling alternator can mean you have a battery on its last legs.

 

I've got a new battery in and still whistling. It's only if it's at idle in a drive gear. The moment any throttle is applied it goes away until it's back in the low RPM range

 

That was exactly the same as my alternator whine on my 70 Mustang 302 V8. It whined when I put it in Drive or Reverse and went away when I started accelerating. In my case my wife had wrecked the car a couple of years before and battery was ruptured spilling acid on the alternator. It still worked but I suspect the acid eventually did something to it.

The alternator as the cause was confirmed by taking off the alternator belt and the noise went away.

 

That's interesting. I'll have to tinker more with my alternator to see if that's the issue. Thanks for that insight!