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Gas tank problems

I have a 97 Buick LeSabre custom. Prior to its insepction last year, it needed a new gas tank. I had a mechanic friend of mine install an after market one (much cheaper than the dealer!) Shortly after that, I kept hearing a loud booming sound, particularly after the car was shut off. I took it to my regular mechanic and he said it needed a new sending unit becuase the old one was creating too much vacuum in the tank which would allow it to contract when the car was on and then expand when the engine was off - hence the boom. (They even heard it with the tank off the car). They put in a new after market sending unit but then the gauge didn’t work. They changed the unit and now the noise has come back. Any suggestions?

I think the problem is the aftermarket tank. Probably doesn’t have enough baffles and internal bracing to prevent the tank from contracting and expanding.

BTW, what happened to the old tank, rust? You live in the ‘snow belt’? I’ve only had to replace a fuel tank because of collision damage. These things don’t get much wear on them.

It sounds like the aftermarket gas tank is oil-canning. One thing to try is bond some sheet metal angle braces to exterior of the tank to prevent the tank from oil-canning. And here’s what I recommend for bonding these braces to the tank.