Engine High Pitch Whistle

[mself]

I recently purchased a used 2012 Fleetwood Bounder 36" class A. It only had 6000 original miles. We have used it about 4 times and noticed a situation that is driving me up the wall. When the engine is under torque (going up hill, about 4000 RPM) and slowing down to about 40-50 mph because of the grade, you can hear what sounds like a high pitch whistling noise. I have the Ford Triton V10 engine which I have had in my prior Class A. The whistling may go away or not until after we top out and the RPMs drop. When on flat surface or from a start pulling the same RPMs it doesn’t do it. Only when going up hills. I have been over the engine and can’t find anything like a pressure valve. Any suggestions before I take it to a mechanic.

[georgelesley]

Sounds like a vacuum leak triggered by low vacuum when the engine is under heavy load. When climbing does the whistle go away when you lift off the gas?

[mself]

Yes it does. Even when climbing it may all of a sudden go away, like the built up pressure has been released. When pulling the same RPMs on level ground it doesn't make the whistling noise. Only when climbing. thanks for suggesting vacuum leak.

[brushbuster]

I have experienced what you describe when towing a boat or Jeep on uphill grades. I always assumed it was the transmission cooler kicking in, but I am just guessing to be sure. Maybe a more mechanical reader will be able to comment. For what it is worth, I have experienced this noise as you described on all three Ford chassis RV's that I have owned and no longer pay any attention to it.

[Waiter21]

Is it the cooling fan clutch kicking in / out.

My fan sounds more like a loud rush of air than a whistle...

[TeJay]

Kind of think of it this way. The intake manifold is like a large wind instrument. As you step on the throttle you are increasing the opening and allowing more air to flow in.

Your noise occurs at specific RPM's (4,000) and climbing a hill under load. Doing the same RPM's on flat ground will not require the same throttle opening. Or if you are doing 4,000 on flat ground you are in a lower gear therefore the load is not as great. It also may be whistling but because of the higher RPM's as a lower load you may not hear it.

Now why the noise?? The flow or air in and through your air intake is causing a vibration. What it is specifically vibrating would be anybodies guess. Here's some things I'd try.

There's a product called Sea Foam that is available from most parts stores. This stiff will clean injectors and the intake chambers of any carbon deposits. It just may disturb something that is effecting the air flow which is causing the sound. The instructions are on the can.

Change to a K & N air filter. There may be something in that area causing the sound.

You may have a vacuum leak. They used to be fairly easy to find by spraying carburetor cleaner in and around the intake but anymore that may be difficult.

There may be a vacuum line that is loose or disconnected. If it is small enough it may not cause any issues but still makes the noise. Just do a general look see under the dog house.

Trying the Sea Foam and a K & N air filter won't hurt anything and it may fix it as well. Worth a try.

TeJay

[mojoracing]

I get more of a squeeling noise when letting off the gas after super high rpm climbing a hill. More like a belt squeeling noise. ANyone ever get that?

[yn1bennett]

I too, in a 1999 F53, Dolphin 36ft, get a squealing sound after it's reached the top of a hill and the RPMs are coming back down.
Could this be the Idle Pulley going bad?
It doesn't do it any other time and only lasts a few seconds.

[mojoracing]

Yep thats exactly what mine does.

[dustyone]

If you are equipped. It may be the turbo spooling down.

[spyderRV]

My serpentine belt will squeak when the transmission shifts because I put an aggressive valve body on the transmission. I think the mass of the pulleys and accessories don't slow down as fast as the engine.