I found very nice quiet grill by coffeebuild. It inspired me to design one that can be printed without supports.
I will report how it works after I have printed it.
UPDATE: This will silence fans that do not run too fast.
Fast running fans I continue optimizing the grill.
This design is good, as you can test the difference on noise levels by attaching the body first, and then the grill.
UPDATE: V2 is identical to the coffeebuild's version. I have not printed it yet. testing soon. I hope it works better with high speed fans (it shall be printed with 0.48 extrusion witdh 0.4 nozzle) I printed it but only effect was that the noise level stayed the same, but the spectrum moved to higher pitch.
Final conclusion is that these designs will help only if you have very high pitch in the noise, then this damps it a bit.
I recommend to print this with PETG or CPE or ABS, PLA is too brittle for the grill.
for CPE is use temps 85C bed, 260C Hotend, on polypropylene sheet
Note use 0.4 mm extrusion width in original and 0.48 for v2
BTW polypropylene sheet is excellent print surface for CPE and PETG. Just wipe with isopropyl alcohol ja print.
After printing the parts - just glue them together with superglue. Depending on the tolerance of your printer parts may just snap together by pure friction