Engine "Harmonics"



ok, here we go: 2004 Ford Expedition, 4.6l V8. The engine makes a loud whistling sound when the engine is warmed up, and the RPMs are around 1800. The vehicle can be picking up speed from a stop or just cruising on the highway. When the rpms reach that 1400 - 1800 range, it makes the whistling noise. It seems to come from the driver’s side of the engine.

I took it to my mechanic, and when he heard it, said it was a “harmonic” noise and tried to figure it out. His best guess was it was something to do with the Air-flow sensor. However since it didnt come up as such on the diagnostic computer he didnt want to replace it just to find out that wasnt the fix.

I live in Fairbanks Alaska and was wondering perhaps the cold air had something to do with it. Dont know. Im reaching out there to see if anyone else has had this issue or has an answer.


I do not know if it is related but my 94 f250 I can play like a flute, our good mechanics thought it might be the egr valve, (ok maybe they give up too soon) I think a second opinion is your best bet unless you can locate the source, give us a clue as to the source and get back to us.


Does this engine have a PCV hose fitting on the intake tract on that side? If so, it should be examined for brittleness and cracking. A whistle could be caused by air being pulled through a crack, or cracks.


OK you are always so good, I’ll check that on my beater with a plow, I guess I am at the point as long as it runs what the heck do I care, it is just extra personality, though I know something is wrong.


Normally a whistling sound indicates a vacuum leak, but that is usually highest at idle or deceleration. Since yours is at a specific rpm, I would suspect an exhaust leak or a heat shield vibrating. Since yours is relatively new, I’d check for a loose or cracked heat shield.


When you are cruising at 1800 rpm, put the gear shift into N, and note what happens to the whistle? {Is the whistle one note, or two/}


I will try that this afternoon and let you know what it does.


My first thought was a vaccuum leak and had it taken into a garage and had every hose looked at. They couldnt find it. I will look into the heat shield.