Originally Posted by M_Six
Those are 100% crops. I never noticed it until I tried to recover some shadow detail in an image taken with my new Tamron 17-50. I thought at first it was the lens, and it does seem to be more apparent with that lens, but I checked shots taken with other lenses and it's there, too. But not with shots taken with the T1i. I don't think it's because of ACR, but I can try it with the native Canon software and see if it's any different.
Those are not high ISO shots. ISO 100 for the 7D shot and ISO 200 for the T1i.
Please try it with DPP. It may not have a local shadow recovery tool, but bring up the whole image to see what happens in those shadows. You can try Sagelight for free, which has local tools and a shadow recovery function.
Could you show the complete image so that we can see the context of the noise?