Toyota Repair: 1996 tacoma gas cap honking noise?, gas cap, trouble code

Question
How do i stop the strange honking noise that my 1996 2.7 5 speed Toyota Tacoma makes when i turn it off. The noise comes from the gas tank, because when i remove the gas cap, the noise stops. I replaced the gas cap two weeks ago with a brand new one, but the odd honking noise still happens. Do you know what i can do to stop it. Thank you. Wayne  

Answer
There is a problem with the tank evap system, it sounds like it is building up either too much pressure or going into a vacuum condition because of a vent problem, I have never experienced a noise like this from a gas cap, but that's my best guess.
Normally a evap system failure will turn the check engine light on, but there may still be a trouble code in the system(pending code)so I would advise to have the system checked to see if there are any codes stored in the ecu.