Sorry for the delay in responding! I took a look, and some of it was post-process (had to +1.85 EV in LR4.1 RC2) which was way too much...
OTH, I had some images checked out at the local photography school in a weekend course I was taking, and even just straight conversion images (RAW to JPEG) in the latest version of DPP, there was a ton of grain similar to this, and the instructor used it as an example of excessive digital noise. Also, in my 550D (t2i) I didn't notice the same issue with finding the proper exposure as I'm finding with the 5Dm3. Just seems to expose everything a touch dark.
And thanks for the comments on my son - he's the majority of what I shoot, but I'm branching out now.
Sensors can be bad. They have lots of on sensor electronics for noise removal, and like any electronic item, can be defective or crippled.
Return it for another, never wait until its too late. If you cannot exchange it, send it to Canon with a example of a properly exposed but noisy image. All digital sensors have noise, even at ISO 100, but it should not be noticible until you get to about ISO 800, and then, a tough of nr might sometimes be needed.
My 5D MK III and my Nikon D800 will produce slightly grainy images when viewed 100% at ISO 800 or over with no NR, the D800 is the worst. NR cleans it up nicely, and as long as its very light NR, the image will remain sharp. As soon as you have to use a lot of NR, resolution suffers, but even then, prints at normal sizes will look sharp.