How to reduce fan noise without reducing airflow?

Question

Iron

There are fans DeepCool x-fan silent 120x120 (120L / B). They are connected to molex, but to 7 volts (between +12 and +5) since they hardly blow at 5 V at all. There is no way to connect to the motherboard. 2 on top for blowing in and 1 at the front for blowing in, on the rear for blowing out (it does not make noise).
Ps I don’t argue, the valves are cheap, you can buy more expensive aerocules for 5k kit and everything will be cool. But can you do something with these without reducing the airflow? Lubricate, etc. etc.? I already attached the valves to the anti-vibration pads and silicone nails.

Answer 1

No way. If the fan is noisy - it will make noise, no matter how you twist it. Only replacement - for example on Noctua.

Answer 2

Balance and grind the blades. But there are no guarantees. It's better to really change.