In a few decades, the concept that someone ever needed hearing protection around a robot will be quite the anachronism, similar to how someone used to marvel that a computer could fit into a space smaller than a large room.
I was going to point out that some robots will always incorporate industrial machinery that would require hearing protection but then I realized data centers are basically building-sized computers. Anachronisms have their place :).
Computer rooms are still loud today and were much louder ages ago. I am not even counting the band printers and such that still exist in many shops.
Back in the late 80s I remember working on what we termed the "Lost in Space" computer. I think it was one of the first models Burroughs created that did not use tubes; the military loved to keep things forever; and it just made all sorts of interesting sounds.
As for robots and silence, oh I am quite sure that some military planners have ideas for giving some special sounds just to inspire fear
