Ford aerostar 2000

i have an engine light code that says fueltank vacuum cannot the van runs there is pressure built up in tank and it makes a noise that sounds like pressure releif valve.This noise happens in fender under the gas fill.I have taken this to the mechanic several times to has light cleared.he hasnt repaired.Is there a part or module in this area that can be replaced.I have never seen something like this in an auto.the fuel pump was replaced last year and this problem has occored regularly since then.I have read that the fuel filter should be replaced when pump is but I have no idea if it was or if it is in tank or at another point in fuel system.i hope this question makes sense.It is embarrasing to drive like this due to the frequency of the blow off