There is a very annoying thump in the trunk that seems to happen whenever I get on the gas or on the brakes at low speeds. I'm almost 100% sure that it's the gas tank as it happens worst when the gas tank is more than 1/3 full. As a result, I never really fill my tank with more than 5-6 gallons of gasoline. However, it still seems to happen when the tank is only 1/3 full!

Does anyone have any idea how to remedy this with modification to the car?

 

let your wife out of the trunk??

looks like you need to jack the back end up (or back it up some ramps) and grab onto the gas tank from underneath... see if it's loose? I assume your gas gauge is working properly? That would rule out a sending unit issue. Also look at the tube leading from the filler neck to the tank to be sure it's not loose.

 

Maybe fuel pressure at the filter?

 

Haha, I just looked in my trunk. I had a big thing of car wash liquid in cylindrical container that was bouncing around.

But the other noise is still there, it's just not as bad or noticeable.

 

Racoons?