Not sure what is actually going on, but I have questions...
1) What are the actual temps when gaming and benching on the 4090? The card is 450w stock and can hit 600w.
1A) Which tempa are looking at? Modern AMD and NV cards report both the GPU temp and GPU hotspot/junction temp and these can vary by 10-20C.
2) What scores/FPS does the card get? Compare to similar setups to see if the 4090 is throttling.
3) Fan Control doesn't need/use a fan header to control GPU fans, but rather the GPU temp as reported by software. It's possible that running multiple monitoring apps my F that up
4) I've had GPUs that had a fan header, but that was used to power a case fan based on GPU temps. It's not an input so don't connect a header from the mobo to the GPU that way.
5) In that HwInfo64 SS, the GPU info will be at or near the bottom. The section shown is the SS is the mobo info that HwInfo warns might be buggy due to the EC Asus uses (Though I've never known it to be a problem)
6) Make sure the GPU power cable is fully plugged in, from the card, to adpaters (if any), to PSU. It shouldn't be possible unless you really force it, but if you are using a 12v Highpower connector to multiple PCIe 8 pin adapter, make sure you are using the PCIe 8 pin cables and not CPU 8 pin.
7) GPU fans are always loud over ~50% PWM anyway...so you need to confirm if it is a temp problem or an expectation problem.*
8) It's possible the card's cooler has a bad mount that makes poor contact between the GPU die and heatsink coldplate, and that mount has gotten worse (gap too large with poor paste contact) over time due to thermal cycling. I would confirm high temps / throttling before I went to the trouble of repasting.
9) Consider warranty service before disassembling.
*The first GPU AIB that ships GPUs with simple 120x25mm fan mounts as stock will print money.