Yeah but the difference between 2 3 4 dB is astounding, there's a formula out there detailing it. To put it bluntly these fans are probably the cheapest available to do the job. For a few dollars more you might be able to replace them with ones that are quieter.

Trying to see what they are but no pics out there other than this.

the whole idea is the reduce the overall sound level where ever possible.  A few dB savings is remarkable on the sound level you hear.

Just looking at the below I would remove that grate obstructing the fans and see if that improves it. You got air whistling through that grate adding to the noise.


http://i0.wp.com/mineforeman.com/wp-content/uploads/2014/03/SPTechBack.jpg