Gas tank buzzing noise

[Jaytbird]

04 LC with 34K miles.....
The oddest thing happened to me last night. I came home from work, parked the car in the garage and turned it off, taking the keys with me. Went to take the garbage out on my way past the driver' side rear of the car and noticed a buzzing sound eminating from near the gas tank door. Looked at the overall vehicle and noticed the lights were still on, so I figured that the buzzing was a light circuit. (A little concerned, but figured it would go a way when the lights were off).
Returned a minute or so later from dragging the trash to the curb, and I could still hear the buzzing....(sounded like a little electric motor), however, lights were off now. Very curious, I ascertained it was coming from the gas tank door...so I opened the door and then it got quite a bit louder, coming from the gas tank cap assembly itself. So....I opened the gas cap, and giant WHOOSH! came out. After that, no more buzzing.
Anyone ever have anything remotely like this happen? Is it a simple vapor build up? Should I be concerned?

TIA
Jay

 

[JERSEY80]

It's more than likely a vacuum on the tank. I've seen a vacuum on my tank when popping the cap just after driving a while.

Then a little air was leaking in through the cap and or vent.

 

[i4c4lo]

You charcoal canister is by the gas tank (older 100's the canister is up front) that is gas venting through the canister. When you opened the gas cap, all the pressure is gone. That is what's making the noise. This is normal, I am sure it happens to others too, maybe they just don't hear it.

HTH

 

[irongrady]

I always hear it after long trips when I am sucking down the petrol. I think its normal....

 

[Jim_Chow]

My '03 does it too. I believe it's the charcoal canister/emissions equipment above the spare. When there's a vacuum buildup in the tank (with engine off), I can hear it right about where the gas door is. If you open the door and remove the gas cap, you'll hear the vacuum suck in, and the noise will stop.

 

[i4c4lo]

It's a lot of gas vapor from all the sloshing around. I think the 100 are more prone to it than the 80 Series. We were in Death Valley a few years ago and we had 4 100's and we all had the same buzzing/vapor out of the charcoal canister. The 80's had some vapor but not as much as the 100's.

I have a 2nd gas tank, at altitude AND off-road I have to keep venting my gas tank, I usually just leave the cap slightly open to let the vapor out or else I will get stranded. The truck will just refuse to keep running. This hasn't happened to just the stock tank.

When it's hot out or your truck has been sloshing the gas around, you will get more vapor in there.

 

[04UZJ100]

It has to do with the gas fumes in the tank, Lovely EPA mandating systems to reduce gas fumes.