much like the commensalistic relationship between skin-stealers and skin-givers, I feel like a similar relationship could occur between screamers and scream eaters, since screaming at loud volumes is a natural behavior of the screamers, I doubt a scream eater feeding on a screamer would do much harm to it.
I also wonder what would happen if two scream eaters tried to feed on each other at the same time. Would it create some sort of feedback loop, leaving the two entities eternally feeding on each other, never becoming satiated? Then again, considering how scream eaters are made up of liquid silence I doubt they'd be capable of screaming, making one feeding on another pointless.