Hey guys, I'm back again with the infamous whistle noise. It's a 5.4l triton with about 235,000 miles on it. The noise seems to be in the front of the motor and only occurs when the vehicle is in drive or reverse. It only happens at idle (500-600 RPMs). The moment any throttle is applied, the noise disappears until the motor is at idle in a drive/reverse gear. The alternator is perfect and in optimal range, it has a new belt tension pulley, and has had the PCV valve replaced twice, and I've sprayed the vacuum lines with carb cleaner and I couldn't find any obvious leaks or holes in the system. Any feedback will be greatly appreciated. My trusted mechanic says it could be possibly the water pump or compressor. But other than that we are all stumped.

The Ford service techs have no clue what it is. I attached a link to a video I shot of it. Sorry it's short

VIDEO OF WHISTLE: https://youtu.be/ycuZmC5GtYY

 

There are several idler pulleys in the belt set up, have you checked/changed those? They have bearings too which could go bad. They're about $20 each

 

All the bearings for the pulleys have all been checked, they all were okay. One was a little bad but it was changed out with a new belt as well and the noise still came back.

 

have you used a stethoscope to isolate the noise?

 

Yes. My mechanic and I have both attempted to locate it with a stethoscope, but to no avail. However, the noise is so loud that it sounds like it's coming from everywhere.

 

Just for fun, take off the serpentine belt and run it a few seconds to see if the noise is still there. Maybe replace the belt if it has been on a while or if anti-freeze has been spilled on it.

 

Will do, I know I just replaced the belt last week. But I'll run it without it and see what comes up.

 

I replied to you in depth as you requested.
Hope you got it.
It is simply an air leak that varies with engine vacuum that is the highest at idle.
As soon as you open the throttle the vacuum level goes down and lowers the airflow leak rate.
Sometimes it's the replacement rubber elbow at the IAC that can cause the issue.
A stethoscope with the long shaft removed will narrow down the area, then you look at all the possible areas.
You just have to try harder.
Believe me, the leak is even worse when on the road and decelerating when the vacuum goes even higher from the weight of the truck pushing the motor through the drive train, with the throttle closed.
Noise and leak velocity are higher and you don't hear it, but it's there.
I do this often to find exhaust leaks.
Good luck.

 

That is excellent! I really appreciate it! I'll be definitely checking that all out! Do you possibly have any other ideas of where the leak might be? I've heard a lot about that elbow piece.

Any good replacements elbows I should look at?

 

Come on now.
I explained it, now your asking me to guess!.
You find it and report what it was.
Good luck.

 

Hey I'm just narrowing down my search 😉 But yes I'll do some digging, I'll let you know what I can find.

 

yep, ya gotta do the investigation.

Wondering if your brake are solid? you also probably have your brake applied while shifting from forward and reverse ....heance the lowest the RPM is and the worst the whistle? IF that is true...then maybe your brake booster is leaking. just a thought

 

They seem to be working okay. I don't see any leaks or any signs of leakage. The tone of the whistle doesn't change. It's always the same and constant. The only time the brakes seem to have a play in it is when I'm pushing the brakes and slowing down to a stop. Which causes the motor to decrease RPMs and the whistle begins.

 

Sounds like an alternator trying to charge a dead battery...

But I'll say a vacuum leak is the most likely culprit.

 

so, anything?