Ford V10 High Speed Whistle

[Merunge]

At the risk of this sounding like a "Click and Clack-The Tappit Brothers" episode, I have these engine observations which don't immediately make sense.
-2020 Tiffin Open Road; 43,000 miles;
-happens with and without toad attached

At speeds above 48-50 mph and RPM's in 2250 range, the engine is (relatively) quiet when even slightly accelerating, but if I take the foot off the pedal, a whistling sound can be heard (>5000 Hz is my estimate).

The whistling sound increases as the speed increases. I do not run over 65 mph.

The sound is not present at high speeds and higher RPM's, likely because engine braking may be occurring(?).

The sound is not present while in PARK and revving then idling.

First noticed sound approximately at 40,000 miles

So far, quick check underneath chassis finds nothing loose (like a shroud or heat shield or ??).

And as far as a fan belt, I cannot even determine a visual location to spot check. I know it's there but I haven't put my coveralls on and really crawled around.

Any 'puzzlers' out there have any thoughts?

Thank you

[Hittntheroad]

Did it just start happening? I know some have had issues with the grills making noises.

[Merunge]

Started about 3,000 miles ago. I will double check that grill! I have had to re-fasten one side already 20,000 miles ago.
Thank You

[boiledowl]

Originally Posted by Merunge

Started about 3,000 miles ago. I will double check that grill! I have had to re-fasten one side already 20,000 miles ago.
Thank You

Maybe a vacuum leak.

[PanJH]

I had similar sound/situation ... turned out to be the bearing on the idler pully for the serpentine belt.

[SergioP]

Have you noticed any change in mpg? It seems like there’s a vacuum leak after the throttle body. The PCV hose could have a small hole in it. When you take your foot off the gas it creates high vacuum, a small hole in the PCV line could make a whistling sound.

[Merunge]

That’s not an easy fix but thank you

[Merunge]

Umm. Maybe 0.1 mpg less but noticed that maybe 10,000 miles ago. I chalked it up to new tires on the toad. I will look, thank you

[winnbrave1]

Sounds like your pcv line has a crack in it. Fairly common problem. Check it or have it checked.

[Merunge]

Thanks for the suggestions. It's manageable for the balance of this trip. I will have it checked when we return.