lol?
I'm pretty sure it's not, though.


snippet from your fullsize image. There's a good bit of color noise in there.

EXIF says it's 125 iso, shot in auto. Even on a rebel it shouldn't be that noisy.
Try shooting uncompressed (RAW) and processing through lightroom instead of gimp.
Or if you continue to shoot in compressed jpeg, turn your noise reduction to "strong" this will help with chroma noise in shadows particularly.