The cheap crappy stock fans are loud in Siglent gear (
With this I don't agree and you need accept that when an instruments cooling is designed for all markets the stock cooling may be excessive for your climate.
The only way to properly address this is to have smart fans and they are fitted into more expensive Siglent gear.
The problem is, that most of the noise occurs, because the fan is not able to press the planned cfm through the mesh.
Not so in an experiment I did recently with a SDS1104X-E by cutting the fan grille completely away.
There was NO noticeable difference in fan noise when the grille was removed.
Ambient temps dictate what can be done to reduce fan noise where in south China not far from Hong Kong 30+C for most of the day is very normal so good cooling is required to ensure long term reliability.
Stock fans have been very reliable and in hundreds of instruments sold just one fan has been replaced under warranty.
If we discount grilles from having a significant impact on noise as I do now that leaves slowing the fan to better suit your ambient temps or fitting a higher spec fan with lower noise. In small formfactor instruments we are limited to small fans with their higher RPM which creates most of the noise.
Careful adjustment of fan speed to suit your climate is the simplest solution at the risk of impact on instrument reliability.