Trumpet or horn sound from gas tank area.

The truck sounds like a trumpet or horn coming from the rear/tank area of the truck.
It usually makes the sound about 5-10 mins after turning the truck off.


I don’t think it’s the EVAP pump or system.
Been doing it for years. Never had any evap codes.
Just curious if anyone else’s trucks likes to identify as a musical instrument


Maybe it’s pressure bleed off from fuel vapor?
The EVAP works off a vacuum test. Suction.
Where fuel vapor creates pressure. Maybe fuel vapor pressure is leaking “out” somewhere, but not “in” under EVAP test (suction)


I have no idea. Just curious if anyone else has experienced this?

 

Maybe post some audio/video. If the description is accurate, I just want to hear it.

 

Been hitting the New Year’s Eve alcohol stash early?

 

Have you tried replacing the gas cap?

 

Wouldn’t that mean it’s leaking,, and wouldn’t that throw a code?

 

I've had them leak and not throw a code. Not a big leak and it might not have leaked when it ran the self test. It's also the easiest and cheapest thing to try.

 

No, I haven’t tried.
It sound like it’s coming from under the truck.

Next time I hear it, I’ll open the fuel door an listen.
Might even open the cap and see if it stops.

 

That’s what I’d think too.

 

How did you know the cap was leaking if it didn’t throw a code?

 

Only time I've heard that is on the Ford cars with the capless fuel fill when the purge valve gets hung open (quite common on those), too much vacuum or pressure in the tank and the safety vent pops off.

 

Customer complaint of a fuel smell. The one on my truck would make the area around it black. I thought it was from fuel vapors. Replaced the cap and no more black.

 

It would be better if we had a video/recording of the sound. If it’s coming from under the truck, I’m thinking charcoal canister

 

It's gastrointestinal

 

Maybe, it doesn’t do it “all” the time. See,s li’e maybe more in the warmer weather.
And it’s too cold outside right now to stand there and eat for it to do.
Maybe that’s why I haven’t heard it as much in the winter.
I’ll not standing there unloading mowers and equipment of the trailer.

 

I don’t know. Just kind of want an explanation when people look at my truck funny and ask what that noise is.

I highly doubt it’s the gas cap. But it could be. Doesn’t sound like it’s coining from there. I almost never turn it into it clicks. If you turn it until it clicks. It feels like you are going to break the cap off. Then all of a sudden a BANG. If anything. My cap would be better suited to keep you from over tightening it.
It’s like 15 or 20 ft/lbs before that baby clicks.

I didn’t even know you were supposed to click it until someone on here replay to try that to fix a 455 code.

 

I mean the only times I've ever heard that it was the purge valve stuck open, easy enough to pop the hose off and check.
I assume it only does it when the engine is running?

 

Nope. Engine off.
And only after about 5-10 mins sitting there.

Sounds like a foghorn under the truck.
It’s weird.

 

Mine does the same thing, I asked the question here and was told that it was the vapor pump doing it's thing. It doesn't effect my gas mileage or nor can I smell gas. One time I removed the gas cap and listened to the noise, it was defiantly coming from inside the tank. I've heard this noise occasionally since 2017, so I just have been ignoring it. Never had it checked for a code.

 

Does your do it like 5 hours after you shut the truck off?

Or like 15-30 mines after.

I can’t recall hearing my vapor pump ever run. But I definitely have heard it on the Lexus. It sounds like a vacuum pump. Not a horn.

Beats me. I don’t have any codes or drivability issue. So I don’t really care.
The only reason I want to know is curiosity.

 

I have the same sound. Mine starts making the sound about 2mins after shut off. It's been doing it for couple years now.
I've pulled the cap off a few times when it makes the sound and it didn't stop.
Sounds like in the tank.
I thought it would be something to do with the fuel pump or back pressure leading back to the tank.

I have no codes or other I'll effects at speed, going slow, or in the mountains from sea level to 1850 m (6000 ft).
I've been crossing my fingers no ills become and totally forgot about it.....till now reading this post.
Should it be addressed or not maybe some one here knows more on that system.