You can hear femtosecond lasers because they ionize the air, creating a spark. They buzz at the pulse repetition frequency.

Do you know how often this one pulses? I was getting the impression it fires once per hour given the power levels.

Big powerful lasers can actually be quite noisy. Once I was talking on the phone with a friend who was working on one of the big lasers (don't remember which one, but it was in the bay area) and he said,"What? What? I'm sorry I can't hear you over the sound of my laser!". When he could hear me, I told him that was one of the coolest things I'd ever heard anyone say.

It's usually the accessories and support equipment that makes lasers loud. Cooling equipment, electrical stuff, etc.

If those can be put in another room then the noise goes way down.