Noise under the car as an explosion - Optra 2006

I have a problem with my Optra 2006 1.8 car, I bought it used as a year ago and did not give greater problem until lately it is giving me problems with a noise at the bottom near the gas tank.

The noise I mention is like an explosion of pressure inside the gas tank, this noise appears after traveling a considerable distance and feels like if something into the car exploded.

I have made him review in some workshops and do not hit him since to vary when I go to the workshop does not sound. Please can anyone give me a guide where can I review my car?

Thank you very much in advance.

I have 2 doubts
, is that noise very often every time you drive?
And at the time of going to a benzineria, does something sound when taking out the fuel lid? As a alibio of pressure similar to when he uncovers a soda drink
because it directly related to an explosion inside the benzine pond that is really discarded unless the problem is not directly from the pond and that the explosions are due to excessive carbon in the catalyst but in this case the engine tenders to stop and you would see that carbon leaves the exhaust pipe
. There are very few data with which I count for your problem

It is true is almost impossible that the noise comes from the kisas pond is in the escape and with the bibration it moves and hits the Estanke of the Estanke is very difficult.

Thank you very much for the answers I already have an idea where to start.

The sound is presented only after driving, if the car remains detained, nothing happens. Nor does it sound when removing the fuel lid.

This morning I paid a lot of sound and happened twice one when I stopped at a traffic light and you see when I arrive at work immediately after turning off the car. Then remove the fuel lid and did not sound like a pressure escape.

When the sound is presented and the car is ignited, it does not affect the engine for nothing is only the sound and movement of the car as something is exploited under it.


Greetings

I don't know but I think you have the answer since all of the above is discarded, it will not be that somewhere in the exhaust tube has a tube union, which carries a spring that presses a nut so that it is always united ( I do not know exactly as they will have already noticed but the idea is that ) it will not be that it lacks squeeze and it has a game when it moves and separates the union of the tube. burst?
Check to rule out all possibilities and let us know how it was