In reply to Apexcarver:
I busted out a real keyboard for this one, so I apologize now if it's a bit....lengthy.
In your time frame, medication might be the best option. The unfortunate thing with panic attacks is there's no instant cure without drugs. The good news is, they have some REALLY good drugs to take care of them in the interim. I can tell you from personal experience, You just don't give a E36 M3 when Valium is on the table. Now, I am not an advocate for medication use, but let's face it, it can help. In the interim, there are several options.
Exposure therapy is a possibility, but you have to do it gradually. You can't just throw her next to a deagle going bang and hope it works out. She's never going to adjust. Start small. Slightly out of her tolerance and work up as she becomes accustomed to it. I'm actually doing a similar thing right now with SWMBO 2.0. Her ex was a terrible driver that thought he was Fittipaldi, so she's adverse to...pretty much everything car. I keep working on showing her that we have control, that the car is made for xxx and so on. If and when I ever get back into cone smashing, I'll make her ride, and eventually drive. Pretty hard to get hurt in a parking lot, in a prepared car.
Beyond that, there's a couple other things to try. Distraction is always a help. IDK if she's actually into racing or not, but if she's not, giving her something to focus intently on can help. First, if her brain is occupied with say....scrapbooking (Or whatever it is women do these days) find her a way to be able to focus on that while at the track. She will be less likely to be anticipating that bang or that boom, and may not even notice it when it happens. Which brings me to the second thing, and one of my personal favorites, something called one-mindfulness. It first made sense to me when someone told me a thing about Buddhism. Buddha was only able to ascend to the next plane of existence because he was able to exist purely in the moment, focused only on what he was doing at that moment. All other problems and worries fade away. Now, if you're familiar with something called "the zone" (pitchers, racecar drivers, all describe it as such) you know what this all means. It means you're so focused, your mind just pushes everything out. All that matters is whatever you're focused on. I find myself doing it all the time gaming...and occasionally when wrenching. If you're doing it right, you can basically be set on fire and not really notice. Almost as good as valium, without the whole schedule 3 narcotic thing.
Really, I know why your wife could feel that way. My ex wife was the same way with loud music. It's a very foreign feeling to have something hit you so hard in the chest without physical contact, that it shakes your guts. Unless you can convince your body that it's ok for it to be doing that, your body is going to go ahead and assume that it's time to go, and kick in with the fight or flight. Think of the times when you're underwater and you know you need to come up for air, but you're still holding your breath, trying to stay down. Eventually the flight response kicks in and you surface. Feeling concussion in your chest is a very similar thing.