I had the EXACT same problem. The stock exhaust is actually fairly decent, and when coupled with the mods you have, and specifically the cold air intake, it makes the car sound ricey. Truthfully, the sound you hear is actually the result of engine resonances which are being allowed because of the cold air intake. If you were to switch back to your STOCK intake, your car would be much quieter. The CAI allows resonances to reverberate all the way back to your tip (which causes the crappy Honda "coffee can" vibration). There is a solution though that allows you to keep the CAI. Like spinner said, you can install a resonator in-line of your exhuast. My advice (personally) is to get an aftermarket exhaust from one of the companies, and cut that up (your stock exhuast is a bit more expensive if you need to replace it). Install a resonator inline of the main pipe that goes from the coupler to the end of the cat, to the muffler.
This will help eliminate some of the resonances that lead back to the exhuast. You'll still have the coffee can sound at some rpms though, and the BEST way to eliminate this is to do what Porsche did back in the 80s when they had free-flow exhaust on their 944s. Basically, you'll want to replace whatever tip is on you car with one that's double walled, and insulated. If you can't get one that's insulated, you can do what I did and install dynomat (the tar / rubber liner) on the inside of the other exaust tip wall. This completely eliminates the vibrations that cause the start of the reverberations and eventually lead to the echoing of the exhaust (the coffee can sound).
I after installing the liner, I taped off the exhaust tip, and sprayed rubberized undercoating throughout the entire inner wall. (Note, I am NOT spraying it in the exhuast, or on the outside. I'm spraying it between the walls of the double walled tip. The exhaust pipe comes out, and the tip is then rolled back along the outside. This part is chromed / polished. This is called double walled. If you install the liner and rubberized undercoating between these two walls, it will eliminate the sound).
The sound is much much better, it sounds really nice, there are no vibrations, no ricey sound, and at wide open throttle, it sounds more like a Porsche 944 than it does a Solstice. I have my stock exhaust back on because I need to weld it all back up, but if you let the rubberized undercoating dry for about 3-4 days, it'll completely harden and you don't have to worry about it melting and draining out.
This is really the ONLY solution. I tried finding a tip, but the only ones I could find were factory Porsche exhaust tips and you had to buy the entire muffler kit (like $1200 bucks) which was NOT worth it to me, so I made my own.
This is why im not Elite yet
