With RSMB by itself it’s hard
You can try this in AE to create some sort of “motion” matte:
COMP1
1. Adjustment Layer
– Levels :: Raise Gamma
2. Source Clip – Transfer Mode Difference
– RSMB Amount 1.0
3. Source Clip
– RSMB Amount -0.5
Then in another comp2 use COMP1 as luma track matte for readding some noise
HOWEVER
It probably works better to remove the video noise first with DE:Noise and then if would want to add some noise after. Another issue otherwise is the noise itself gets motion blurred which might or not be OK.
Pierre