I upgraded from my XTI with the 28-105 USM lens to the 7d with the 28-135 (130 maybe) USM IS lens. I'm just getting it unboxed and getting familiar with some of the buttons, etc - but i've noticed that the camera seems exceptionally loud while firing off photos, and the lens seems loud while autofocusing. That may just be a case of "that's the way it is," but shouldn't a newer, more advanced camera be quieter? Or is that just me showing the noob-factor? Thanks
In addition to @Guffa 's great answer, the Canon 7D does have two silent shooting modes. If you are in a situation that you are concerned about the noise that your camera is producing - that is exactly why they now have these modes. You do tradeoff performance in either speed of the shots or AF - but if you just need to take a quiet shot in a church for example it is a great alternative.
You have two modes, Mode 1 and Mode 2. Mode 1 leaves the shutter curtain open while you shoot continuously. Mode 2 is for single shot and just lets you decide when to reopen the shutter. Try them out, I think this will resolve your concern about any additional noise, as they are considerably quieter options then the standard modes.
A newer, more advanced camera isn't neccesarily more quiet, because the sound level is not so high on the priority list. Simply put, quiet cameras doesn't sell better. (Well, at least not compared to other features.) Actually, more advanced might mean that it gets louder.
If the sensor is larger, then there is also a larger mirror, so flipping up the mirror makes more noise. Also, if the delay from pressing the button until the image is captured has been cut, the mirror has to move faster, which makes it louder.
If the auto focus is faster (which it often is on a newer camera), it generally makes more noise simply because the motor has to do more work to move the lens elements faster. Also, if the lens has larger lens elements (to allow a larger aperture), then there is also more mass for the focus motor to move.
The max shutter speed on the 7D is 1/8000", while on the XTi it's 1/4000". That means that the shutter itself moves twice as fast across the sensor. It's possible that the mirror also moves faster on the 7D than it does on the XTi. Both lenses should be fairly quiet as they both have USM motors, but the image stabilizer in your new lens may contribute a small amount of additional noise.
The Canon 5D and 6D have "silent" modes which actually slow down the mirror and thus reduce noise somewhat. The 7D takes a different approach -- it's "silent shooting" modes function only during live view, i.e. when you're using the display instead of the viewfinder.
The sound you here is louder because the Canon EOS 7D is built tougher than the XTi. Its shutter is rated for more usage, faster shutter-speeds, faster continuous drive. Plus, most of this applies to the mirror mechanism too. A faster moving mirror gives you a shorter black-out-time which is highly desirable. This tougher mirror and shutter makes more noise which is what you hear with every shot.
You can use one of the quiet modes to slow things down and you will hear the difference. Things move slower, so they make less noise.
Your former lens is very quiet, I have one of those. I have seen your new lens but do not recall if it was louder or not. This may be simply mechanical differences as well.
I would suspect the reason is purely because the mirror moves much faster, thus it makes more noise when it stops.
The 7D can fire 8fps. So the mirror is designed to be raised and lowered 8 times per second, with enough time in between to give the camera a reasonable chance to focus. This means that the time to raise and lower the mirror has to be much faster than 1/8th of a second.