Last obvious observation.

Spec. the actually system fans. You have to think that in the design and build, consideration was not given to dB levels since it seems the purpose in mind from the outset was data center compatibility and cost effectiveness.  There are million and one fans out there. Spec. the 6 fans that are currently in the box and find a quieter alternative. Fans are dirt cheap.  Increase is minimal for quieter fans. 45-50 dB is the sound of an air conditioner. 58 dB is nuts.