Just a little tip for anyone reading this. You can silence/quieten any fan by putting it in a cardboard box stuffed with old clothes and using accoustic ducting. I've been doing this for years. I tried the usual ways with mdf boxes, expanding foam, bungees etc etc but found using old clothes and a cardboard box worked much better, lol. Also, instead of attaching your filter directly to the fan, run a length of accoustic ducting between them to eliminate the fan noise coming through the filter.