2750 appliance environmental info

[flexnet]

Dear Opnsense HW users, I am a new user of the opnsense distribution and I am thinking of buying a dedicated unit for this FW OS.
I chose the 2750 model because my requirement is to rack mount it, but after reading a comment from another user, I think the noise is very loud, what is the real sound impact? Last year I managed to modify a cooling fan of a lanner unit (Atom C2000) with a superb result.
Does anyone have experience with these devices?