I wrote this summary of things one should consider while looking to buy and auditioning an exhaust system in another forum and thought it would be a good idea to repost it here. Have fun reading.
BTW, after close to 3 years with the Cargraphic, I still consider this one of the most important upgrade to the Turbo. I have had absolutely zero problem with this exhaust and still recommended it without hesitation. The sound is really, really fantastic.
1. Web sound clips could be extremely misleading so always try to listen in person. Reason for this is that there is no standard whatsoever on placement of mics, what type of mics, volume level, where the recordings are done (inside vs. outside), playback volume & system, etc., etc. All these parameters have significant influence on sound. Just think: by merely cranking up the bass of your computer system, you could change how an exhaust sounds!
2. There is no single best exhaust on the market with respect to sound and you should question anyone who advises you otherwise. The reason is simple: exhaust sound depends on multiple "parameters": loudness, frequency, character (staccato or continuous), etc., and just based on loudness alone, there simply cannot be a single system that is right for all, no? Get opinions from forums but in the end, trust no one except your own ears. You have to listen for yourself.
3. In-cabin vs. out of cabin sound. Not many talk about this topic, yet it is one of the most critical aspect of exhaust auditioning. In *all* exhaust systems, in-cabin sound (listening from inside car) is quite different from out-of-cabin (listening to the car from the sidewalk). The in-cabin sound is a. not as loud, and b. has less of the extreme ends of frequency response. Therefore, out of cabin sound is nearly always more aggressive, louder, deeper; basically "better." So therein lies the problem: While the out-of-cabin sound is better, the in-cabin sound is what you hear most of the times. This makes, again, a live audition from inside the car critical.
Let me give you an example and see if it makes sense: In my car without question the best sound is out of cabin: WOT on a narrow street (for reverberration LOL), with me standing on a sidewalk. It's a spectacular sound show, a cross between a jet taking off and a race car. However, in cabin, my favorite sound is actually at Stop signs, when I apply a quick jab of partial throttle to 1500-2000 rpm. Here, the exhaust gives an unbelievably satisfying, deep throat purr and then a howl as I let go. I still to do this, to this day, all the times at Stop signs. People look at me like I am a juvenile delinquent, and juvenile delinquents look at me to check if I am asking to race them. At higher rpm, the sound is muscular, similar to GT3, and indeed better than stock, but it's not something that would get me very excited.
4. Power. I know there have been dyno's showing gain of such and such, basically from a more free breathing catalytic converter (stock 600 cpsi cell density, most after-market 200), but in reality what most people feel is simply a faster spooling up. The tach needle *seems* to go up faster, and that's about it. There are actually some anecdotal reports that one could feel a loss of torque in the low range by just adding an exhaust system. I don't know whether this is true, or if it is consequence of seeing that tach needle moving up quickly.
If you want power, get an exhaust AND an ECU tune. Exhaust alone won't do anything worth mentioning, and in fact may cause a sense of torque loss -- see below. Any rave about power gain is more often than not unproven with dyno and more likely in someone's head, IMHO.
5. Sense of torque loss. This is not often talked about, but it's there: There have been reports that there is a sense of loss of low end torque with an after-market exhaust. The few cars that I know about are interesting in that it involves 3 different brands of exhaust, 2 from Europe and 1 from the US, one is auto, the other manuals, so there is no trend. In one case, owner (who used to post here) had dyno that shows a drop in low end torque with the exhaust. Whether we could trust these dyno's (done on different days), I am not sure at all.
I don't want to make a big deal about this because the reports are anecdotal and could be a subjective sense stemming from the faster spooling up with an after-market exhaust. But yet, there are tuners who have told me that yes, this is absolutely possible: Reduction of back pressure *could* cause torque loss in the low end. So... beware and be happy if your after-market exhaust feels the same as before, don't even think about power gain!
6. Convertibles have less sound proofing than coupes, so keep that in mind. Some people prefer a more quiet exhaust system like Miltek and Tubi for convertibles, some want the full loudness. It's strictly a matter of personal preference, no wrong or right. It also makes it even more important to try to audition a car that's as similar to yours as possible.
7.Other components in the car affect the sound, and you will be very surprised what could affect the sound. An ECU tune could make the sound louder and take on a high strung (more high frequency, less warmth, louder, more stressful) character. Similar to pushing that "Sport" button, but a little louder. I believe this is a consequence of changing timing & AFR.
8. Resonance (often erroneously referred to as "drone"): Enough ink has been spilled that it's almost mandatory that the audiophile in me add a few comments, from having listened to several exhaust systems in multiple cars, as well reading numerous posts on this topic. Resonance is a very subjective description and means different things to different people. To me, and most sane people, it is an increase in noise level, and in the case of the Turbo, this is most frequently in the 2400-2800 rpm range or so, and almost always in the higher gear, from 3rd and up. Even the stock exhaust Turbo has a mild version of this. The resonance in the stock car is heard in 3rd gear and up as a mild and louder hum, almost like the engine lugging noise. As you replace the stock exhaust with an after-market exhaust, this small hum noise becomes louder. The louder the exhaust, the louder this hum becomes.
If you search the forums enough, you will see that resonance/drone mentioned with nearly every single after-market exhaust out there, from Cargraphic, to Tubi, to Fabspeed, Europipe, AWE, etc.; the list goes on and on. Any tuner who claims otherwise IMHO is not telling the truth, or has a different definition of resonance, or doesn't know what to listen for. That said, in my experience, the noise is louder the louder a particular exhaust is, and the more low frequency it has. This is a fact of life: If you want to have a nice sounding and medium loud exhaust, please mark my words on this: It will have a resonance. A very famous exhaust I have heard that has the least resonance is also way too quiet and has no low frequency punch to speak of (I didn't like it at all.).
Also important to keep in mind, the mods you put in your car, like stiffer suspension components and ECU tune,could increase the noise level and could make the resonance worse.
In the end, why is it not a problem with a majority of exhausts people are using? Answer: The way we drive and the way we adapt our driving. The Turbo power kicks in at 3000, so most of the times, the shift, if you are a "good" driver :-), is done at above 3000. Basically, you do go through 2500 rpm in first gear, but here because it's low gear, there is no resonance, then from then on you will hardly see 2500 again until cruising level. And if you are a good Turbo driver, you don't cruise at 2500. The fact is this: I am a particular difficult and finicky person when it comes to sound, and I've had the Cargraphic for a few years now without any problem. If yours has a problem, check the installation, or check other mods that you have in your car, like an ECU tune that could cause a bad interaction.
9. Idle versus WOT: A very interesting issue. Since this is not a race car, you actually want a quiet idle. That's right, these are the requirements of a good exhaust system: Quiet at idle, only moderate noise at 3000 rpm cruising, and really loud when throttle is open. Particularly because this is a daily driver, you do not want a loud idle because you will be sure to come home with a headache.
10. Tunnel Audition: As mentioned above, frequently the best sound is from outside the car, and the best way to do it is to have someone do a fly-by of your car at WOT, with you standing in the sidewalk. Since most of us wouldn't want someone to abuse our car like this, is there an alternative? Happily, yes and very simple: Take your car to a tunnel and accelerates through it in lower gear (so your speed is appropriately safe) to 7000 rpm.
You have not lived until you drive your car at WOT through a tunnel with windows down, and sunroof down. I promise you will come out with a silly grin, but beware that other drivers in other cars might not be pleased and in fact might even flip you the middle finger (in the US). It's really best to do it when there is no other car around. I have found this to be an amazing stress reduction exercise; very therapeutic after a long day at work 
for example.
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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Custom Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! 
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of a Cargraphic exhaust. A co-worker (male of course, 99.9 % of women don't like loud exhaust) came up to me a week ago and told me the sound is "spine tingling." Did not make this up, guys. LOL.
In general car guys, even seasoned Porsche veterans, CANNOT have enough of the sound of this Cargraphic system. Menacing yet very sweet.
