As soon as the PSU heats a bit up, the fan spins fast enough to be in the expected range.
That sounds like a sick (in the old fashion use of the word) PSU. You need to find out what is changing when it heats up. Is it the FAN heating up, or is it the PSU. If it were the latter then it needs replacing as they should not do that. It also applies to fans.
It looks to me like you are getting your early warning now.
Huh? Nothing wrong with the PSU doing that, it is supposed to do it. It is regulating the fan's rpm depending on the temperature.
The fan is spinning at a constant speed at any voltage, only problem was that at low voltages, it was spinning slower than the stock in the PSU. As soon as it gets more voltage it is exponentially speeding up with a linear rising voltage. That is why it only beeps while the PSU is running it at the lowest voltage the fan controller in it is made to do.
Sounds like a standard heat controller fan PSU to me.
Most PSUs these days have a build in fan controller that runs the fan at slow speed when cold, then if/when the PSU starts heating up (like when your computer goes from an idle load of 50w to a full power load of >300w) it spins the fan faster.
Probably 90% of the non-crap PSUs sold these days do it.
Yeah, except this is temperature controlled.
It is an Enermax Galaxy 1000W, and it should be pretty good, and when I look inside it, it is also very tough build when I compare it to some cheap PSU's I got. Sadly they saved too many money on the fan's used in it.