What's p with car making sounds like gunfire?

Dear Tom and Ray: I have a new 2005 Chevy Tahoe LS that I just purchased, and the entire time that I'm driving -- and even after the car has been shut off and I'm no longer in the vehicle -- there are very loud bangs that come from somewhere under the car. It's extremely loud and sounds like gunfire. I'm told it's the catalytic converter expanding (or something like that). The dealer says that it's normal, yet I don't hear anyone else's Tahoe making these noises. It's quite embarrassing. Ever hear of this, and is it OK?

Steven

Tom: Are you sure you're not driving in Iraq, Steven? Because if not, you shouldn't be followed by the sounds of gunfire every time you drive.

Ray: It IS normal for exhaust systems to expand and contract. When they do that, they often make popping or banging noises. If you've ever lived in an old apartment building, you've probably heard the pipes banging when the heat goes on and off. That's the same phenomenon.

Tom: But two things you say make me conclude that it's not just your exhaust system expanding and contracting. One: The noise continues the "entire time" that you're driving. Normally, you might hear this for the first minute or two of driving or, more likely, for five or 10 minutes after you shut off the engine. But hearing it continually is unusual.

Ray: Two: You say it's extremely loud, and sounds like gunfire. I've heard it described as pinging, ticking or even clanging, but never as some kind of assault weapon.

Tom: Your dealer has given you the time-honored response "They all do that." I suppose that could be true -- although I can't imagine they'd sell many Tahoes, in that case. So I suggest you test the dealer's theory.

Ray: Start by going back and asking the service manager to take a ride with you. The dealer may be basing his response on your description of the noise, rather than on the noise itself. Once the service manager hears the noise, he may say, "Wow, it shouldn't be that loud -- that's something else." Or he may say, "They all do that." Tom: If he sticks with his story that they all do that, ask to take a test drive in another '05 Tahoe. If it's quiet, then you can insist that they fix yours, because clearly they don't ALL do that.

Ray: But if the other Tahoe does make the same noises, then I guess the dealer is telling you the truth, and you'll just have to live with it. Maybe they all DO sound like they're spraying gunfire as they drive down the road. Maybe it's a brilliant new anti-theft system GM has come up with.