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I was getting quite jealous of seeing (hearing) everyone else's rumbly Imprezas around the area, and so about two months ago I went ahead and bought a brand new Invidia Q300 for my 2011 WRX hatch. It's quite good looking, and definitely good quality, so I was excited to get it on the car when it finally came in the mail. Installation was pretty easy, I did it in the parking lot of my apartment with a jack and a few basic tools, just two days before driving up to Wellsboro, PA for STPR 2012.

Starting the car up the first time was when things first seemed to not be as I expected. The Q300 is supposed to be the conservative alternative to the traditionally loud N1 style exhausts. But this thing roared. Sounded quite awesome though, so I didn't mind at first until I took it on a test drive.

It was pretty awful. For being a "conservative" exhaust, it was stupidly loud. You couldn't hear the radio at all if it was set at anything less than 30/40. Conversation was impossible. The low rpm drone was beyond headache inducing. it would rattle your eyeballs in their sockets as well as let you know how cheap the interior was put together. Everyone I had in the car with me said it was awful and I needed to go back to stock, and the drive to PA was only possible with large amounts of tylenol. All in all, I hated it, and was planning to sell it rather soon.

About two-thousand miles or so later, the exhaust has completely changed. I can use the hands-free bluetooth feature now, the drone has all but gone away, and it's also quieted down a huge amount, down to the level that I had originally expected the Q300 to be. I know it's not just me going deaf, because other people have commented on the change as well. I still wouldn't call it a quiet exhaust, but it's an acceptable volume, and I don't feel it will attract unwanted attention like when it was first on the car.

I still can't believe how much quieter that it has gotten. Is this something that's usual for breaking in a new exhaust? If so, it's definitely something that should be mentioned more often.

That's a bit more miles that I would expect, but this is completely natural behavior.

I would say it was close to 1000 miles before I really noticed a difference, but it's continued to get quieter since.

it usually takes just a few hundred miles. and, there's usually not a HUGE difference in volume; if its loud when new, it will be slightly less once working properly.

I think that is weird, not like anything I have ever experienced.
To guys who say this is normal: Does something physically change in the pipe? I could understand if the ECU changed the timing a bit and would change the pulses, but short if the actual internals of the exhaust changing, I don't see what could account for the change.
Help?

Oh it is extreme just not completely unheard of. There is a physical change happening in the packing in the muffler. The application of exhaust gasses to the packing will mellow the sound.

I can see small changes happening, caused by the material heating/cooling a couple of times.... but that dramatic? Hmmmm, does sound odd.

Depending on the construction materials I could see perhaps a small change in tone or even a slight decrease in db levels, but I suspect something else is going on. Is this a Full TBE? Have you noticed any performance changes? Quicker / slower spool-up? Perhaps the cat has expanded with the heat and is creating a bit more of a restriction and thus dropping the volume down. I'm shocked that this would occur. I've never heard of an overly loud exhaust getting quieter.

I've had an aftermarket downpipe/tune with the stock catback for about 6 month before I got the Q300, making it a full TBE. It was a used catted downpipe when I got it, even, so it should be as broken in as it's going to get. I've not noticed any changes in performance, car has been running great the whole time. I'm not worried about it, just curious.