I would not recommend modding the PSU. It got high voltage inside that can hurt/kill even after unplugged.
The Framework Desktop Deep Dive: Power Supply blog mentioned Noctua fans are not sufficient to cool the PSU and the current fan is the best all around. So there is probably no point to replace it anyway.
The blog also mentioned the fan should ramp up to the target rpm gradually. There are some reports that this didn’t happen.
that turns 100% on / 0% off without the RPM ramp that was promoted in the PSU deep dive on the Framework blog
from this post