It's not brown noise, my educated guess is that it's semi-transparent areas in your video.
In After Effects under the viewport you'll see an icon of three circles, click it and select alpha. If you have your background turned off, you should see a black and white image of your matte and you'll probably see the holes and rough edges.
Beyond all the details of processing greenscreen, the main pieces of advice I have is two-fold:
1. Whatever footage you're converting from, convert to uncompressed. You don't want to mangle footage with another round of compression; greenscreen footage is very sensitive to the issues that compression introduces.
2. Denoise your video with something like Neat Video. This issue seems to be some level of yellow noise which is similar enough to a green hue to cause some semi-transparent holes. Denoising also helps blend colors and will improve your key matte overall.
the noise is originally transparent, but then i use the clip white/black options and that solidifies it, but the noise just gets more noticeable.
As for not compressing the video, i cant figure out how to do it in the video converter. Do you know of a good one? most video converters do something weird (don't know what it's called) that makes it "squish" when i bring it into after effects.
I am Pretty much self taught when it comes to this stuff, so i don't know allot of terminology.
The weirdest part is when i go BACK into AeCS5 and try to key it the noise is still there! Im doing the same thing i did 8 months ago and it gives me noise now, any suggestions?
you can see the old video here:
-ignore the first shots, they are REALLY messed up. the lighting was horrible near the treadmill.