I took the screws out of the fan and mounted it on sticky pads. It doesn't make it silent but it stops it resonating so much... Removal of the fan seemed ok for a few hours when I tested it but I wouldn't be comfortable suggesting this long-term....
I have an SPA112 which is silent (no fan) so I was amazed by the noise made by my SPA8000. The problem is the grill, or lack of it, in the side of the case. The fan itself is whiny but fairly quiet in free air, but when near objects, or pressed against a surface with less than 50% holes, and square edges, makes a lot of noise, and has a significant effect on the air flow.
I have voided any warranty on mine by removing all the circles in the grill section, leaving just the radial supports for the centre. I would have preferred to remove the lot, but that would leave the fan too exposed. The fan does not have to work as hard now, so I put a voltage dropper in the lead to loose about 3 volts. Now it is a lot quieter, ant if anything, appears to be running cooler than before.
Maybe a revised enclosure could be used with the fan exit cut-outs changed to give less obstruction to the air flow, without endangering the fan or users, and a lower powered but quieter version of the fan.