We have been using a ARRI > DPX workflow where we need to use AE's color management. We set our working space to sRGB, and color depth to 32bit, so we can interpret the DPX plates (which are in log - this prepares us for a roundtrip back to log).
Upon first bring this setup into 2017, the color of both the footage and any effects was looking horribly noisy/grainy and banded. I figured this had to do with DPX or something, but I did some more testing.
It seems that simply setting the project working space to sRGB or Rec709 etc creates the banding/noise, no matter the color depth or what the source images/effects are.
Whats up with dis???
Also to note - the color seems to be ok on export, but its not viable to do work off of such reduced preview imagery.
For now we are rolling back to 2015.3
Does the banding/noise you are seeing go away if you disable the "Hardware Accelerate Composition, Layer and Footage Panels" Display Preference?