I've got a Rena Air 100, it is quiet if you restrict the airflow (I can't hear it). I almost took it back to the store due to the racket it was making (I bought it to replace a noisy pump) and then started messing around with a clamp on the airline, hey presto - bliss silence
(about 50% of the initial throughput).
Maybe this an answer - get a pump with a higher capacity than you need or want and restrict the flow.
I don't know why this worked or whether it is good for the motor in long term.