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PSU fan runs at full speed
(lemmy.world)
Are there any switches on the psu itself? Whats the exact model of power supply? "750W EVGA" tells us almost nothing.
RMx Series™ RM750x — 750 Watt 80 PLUS Gold Fully Modular ATX PSU (UK)
That's a Corsair PSU.
See also this: https://www.reddit.com/r/Corsair/comments/kt81io/corsair_rm750x_fan_spinning_at_idle_half_of_the/
Link to Reddit sadly, but more people seem to have "this issue". If you also have a GPU in there, you might just be taking too much from the PSU to idle.
Does it actually post and boot?
An exact PSU model would help tremendously, afaik only high end ones have variable fan speed, for example my cheap Thermaltake's fans spin at constant rate