Yowsers! Sounds like a hamster fell into the PSU fan blades. Must be all the power spiking being talked of with the 4090s as my 3080 can pull 340W with my 750W PSU all day long in near silence and your 4090 is pulling less than that. Either that or your PSU fan actually does that have an obstruction in it that is being triggered by a higher fan speed, because that doesn’t sound like something electronic being stressed.